In the spirit of research I have taken it upon myself to play a lot of games that delete 3 identical neighbouring items for inexplicable reasons. These are my findings.

I stuck to iPad games where possible because I'm lazy.

Puzzle Quest 2

Match 3 with spells against an AI with lots of tedious exposition. I would've expected at the very least playing some genius word swapping Twine game in between Match 3 battles. Otherwise, why bother, you're just blue-balling me. Swipe detection is a bit ropey.

I first tried Puzzle Quest on the DS. I didn't get it. It just seemed like a cumbersome take on Match 3. Now that I've played 868-Hack I see a layout in this iPad version that I recognise. And this bit of Puzzle Quest 2 is really good. The battle aspect is a great objective and in the spells there's something that freemium boosters fail to deliver: a calculable advantage. It's just a shame that I won't see myself introducing many people to this because the actual quality bits of game are all padded out with a load of generic RPG pish.

Zoo Keeper

Collect matched items against the clock. Drops one-touch colour bombs for power ups. Shuffles quickly. Increases colours with levels. Doesn't hold hands.

Zoo Keeper has the chunky trappings of a Gobot yet its arms refuse to fall off, its decals go unblemished. It's hard not to like it at a basic level. I'm not a fan of a time based premise however, so I recommend it, but it's not really for me.

Candy Crush Saga

Match 3 with power ups for complex matching, environmental level objectives and mild F2P bullshit.

I've already written about this. So have a lot of other people at the time I'm writing. I stand on my opinion that evil is not so black and white, and there is entertainment to be had in the game by way of thinking of CC as a punitively hard title. Good on them for making a hard game. I look at it now and its pay-to-win tactics seem meagre compared to other freemium games (and yet more successful). But I know it used to be much worse. And when I run out of lives and quit to the level screen it shows me an advert for much worse.

Farm Heroes Saga

This is basically a Candy Crush clone relegated to the quantity of matched items objective. Matches add one turn bonuses to neighbours. I hate this game.

CC is evil, but it's an evil you respect. The prices are transparent and in your own currency. It has a lazy pace, and the end of level chaining is tedious. But it's for lazy people, I'll let the automated bonus round of score slide. The graphics aren't award winning, however their communication is sound. I know what's going on. I can spot matches very fast and plan cascades.

So basically take all of those points and turn them on their head. That's the heaving piece of shit that is Farm Heroes Saga. I'm in actual pain when I try to play this game.

It has interchangeable and recondite in-game-currencies. Similar to what English money used to be like before 1971. It takes the simple demand of asking the player to pay to possibly win a level and tries to make it subliminal. I don't buy it.

If you have moves left after winning, you have to play through them all. This is how they've addressed their obsession with the 3-star system. You've completed the level, now you must play through purgatory before you have any more content. I believe I was once offered a booster at such a point where I had completed a level with 30 moves yet to go. Then I "scored" more moves. Stop. I want it to stop. I did what you asked, why won't you leave me alone?

Logically faces-on-godamned-everything should work here as face-spotting is a human gestalt. But they keep bloody winking and jiggling and smiling and goofing off. It's off-putting, especially when the hint system is an imperceptible jump. What moved? They all moved.

Avoid.

Bejewelled HD

Feels like a CC prototype in this day and age.

Has a plodding reliability to it. Even in the other modes the mechanics are a constant, they never change. Its Zen mode is a nod to this truth - I can be boring but I am content to be boring. That is what I am.

I like how polished it is. Hint button is damned handy. The score mining objective I'm just not into. And that's pretty much all they offer.

Bejewelled Blitz

Hey, do you like Bejewelled? How about a confusing in-game-currency to buy a higher score? Started messaging me, even though I'm sure I turned that off.

Bejewelled 3

Same old with more modes.

Didn't offer me anything other than what I'd already seen on the iPad. The other modes didn't really explore whatever new mechanic they introduced. But then I find this in the quest mode: Poker. There's a lot of strategy in this. It's almost like the deck building that goes on in Puzzle Quest. But it's a lot easier to grok, so you can enjoy it without being an accountant. I wish there was more of this sort of thing.

Triple Town

Plonk down random tiles from a deck. Match 3 neighbours in any direction to collapse into a new colour. I avoided Triple Town because of the pack shots - its fuzzy bear didn't sell it to me. I've never been particularly sold on bears. I had a stuffed toy frog as a child.

I've played it and I can see the appeal now. It has a sort of Carcasonne type of charm. It's a nice and Zen little task that reminds me of the now infamous match-em-up Threes. Couldn't care less for the in-game-currency. Was happy to pay for more modes though. 5 modes or more is a good sales item, I don't mind paying to explore a mechanic throughly.

Alien Hive

Triple Town with sliding tile puzzle rules for movement and match 3 gravity. I wish the negative space was more visible.

It's at first a charming little core, but then has the weird gall to start hassling you for change through strange boosters. Worth playing for the central puzzle.

Push Cat

Match 3 gems to turn them into coins. The titular character ignores gravity whilst almost everything else doesn't and can push horizontal rows of items. Collect enough coins to qualify.

I sort of like it, but then its boards are needlessly big. It reminds me of DROD. You've got a reasonably elegant mechanic that could explore a lot of these ideas atomically but it just gives you a massive map. Turning what should be a nicely rounded task for a level into a grindy slog.

Tetris Attack née Panel de Pon

Open top match 3 board with crappy d-pad cursor and only horizontal swaps allowed. You can swap anywhere - even into open space. @HilariousCow referred me to this one. I found an online SNES emulator of it. It had six votes on its quality, all of them 5 stars.

My complaints are that the pace can be slow in comparison to modern games at times and the cursor movement is cumbersome. That's it. The endless mode is nice and Tetris like, the puzzle mode is at first insultingly easy and then scales up into Mensa territory. A lot of match 3s rush to fill the negative space, as if the game can never progress without it. Yet negative space is a mechanic in itself, and it's explored excellently in Panel de Pon. We can only hope that when Nintendo elected to try developing for mobile they mentioned this game at the table. Long live Panel de Pon.

(@vectorpoem has pointed me to its current nom de plume Planet Puzzle League. Probably because Americans think "Panel de Pon" sounds a bit gay.)

Money Idol Exchanger

Match by swapping a la Pang. Only got a video of this that Dennis Au sent me.

Looks interesting enough.

Puzzle Bobble

Match 3 to drop multiple hanging items.

I have fond memories of Puzzle Bobble. They were sullied recently by playing Bubble Witch Saga. There's no substitute for the classic in this case, but substitutes are all I can find.

Columns

Match 3 diagonally as well as horizontally with stacks of 3 random items falling tetris-style.

I remember seeing this as a kid on my mate's Sega and thinking, oh is this some Tetris rip-off? It turned out it was its own solid little title. I don't care to play the phone version.

Meteos

Match 3 to activate rockets that carry items above upwards.

It's a quite a fun little columns variant. Doesn't hold my attention for long though.

Puzzle and Dragons

Drag an item anywhere on the board to match 3 items to activate JRPG attacks from your pokemans.

@rclarke kept banging on about this one. It's efficient, I'll give it that. There's also a lot of content in the way of collectible monsters, community stuff and F2P bullshit. I don't like the gem dragging mechanic. It's inconsistent and they know it's inconsistent because when I tried scrub-moving gems with one in hand it eventually put a timer up to stop me cheating free matches. A deep game with deep issues. Worth trying.

Jewel Quest

Match 3 to Q*bert the board. Its current incarnation on the iPad is a Candy Crush clone.

There's some nice levels in there. A lot of shady F2P as well. I did like matching for item poking boosters. Felt like collecting spells.

10,000,000

Slide columns and rows to match 3 to perform tasks against a clock.

I met the guy who made this at a London Game Dev Lunch. He was waxing lyrical that you had to approach the gaming press with a story. Some drama like Super Hexagon being refused into the app store that one time will get people talking about your game. I consider my own situation now and wonder why I'm doing it all backwards and getting people to read about match 3 six months before I have anything to show.

It's a timed game and it's grindy. I think there's something there for other people, not me however. I like my clock turn based.

The Candy Jam

There's some interesting satirical takes on match 3 in there. I think I enjoyed Sticky Candy Puzzle Saga and its tight little levels the most. Look and learn Push Cat.

What Have We Learned?

Popular variations on match 3 have used collapsing and negative space to the best effect. Deck building goes great with the resource mining aspect of match 3 (868-PLAQUE misses an opportunity here to be an amazing variant on Brog's little wonder). Boosters are an apology for broken level design, spells on the other hand add variety to the gameplay. There's exploration of limited inputs out there (my own experiments included) but when match 3 designers get ahold of the touchscreen they keep pushing the boundaries of what you can poke. They often clutter the real estate with experimental business models. Only Puzzle Quest (of what I've tried) takes advantage of this in the service of engaging mechanics. Then it starts rambling about a D&D fan-fic it wants you to check out.

What works best for matching 3 among them? Clear and identifiable items. You needn't paint a rainbow but make items unique. Hinting (don't start bashing me for not being a bird of prey, I'm old, I've got duff eyes and it takes a while for me to see things). No time wasting - examining the board is the fun part, looking at each colour group in turn. The rest of the guff may help illustrate rules or tell me I did done good but you know what I came here to do. Let me play the game. And last but not least: Content, lots and lots of content. Being a gambling genre, match 3s are as replayable as roguelikes. In other genres this would be padding, but in match 3 it's really enjoyable to explore the myriad of possible boards and the effect they have on the game. Call it the Nethack effect.

I'm still learning Unity's idiosyncrasies right now so it will be a while before my own take on the genre with its own way of manipulating the map will hit the shelves. Do try out the good ones I've mentioned if you've been sitting on the fence. And if I've missed out your own amazing match 3 game, then yeah, now you know how I feel whenever I read most articles on roguelikes.

Further reading:
https://www.jesperjuul.net/text/swapadjacent/
http://tvtropes.org/pmwiki/pmwiki.php/Main/MatchThreeGame