I'm coming at this as something of a novice. There's something I really like about pinball, but I'm not that great at it, nor do I have any nostalgic love for any particular tables. Anyway, Pinball Arcade is brilliant in the way it does demos, enabling you to play up to the high score before you buy anything, and that gives you a good go at each table. On iOS, you get Arabian Knights for free, and I also really enjoyed Ripley's Believe It or Not (nice layout, lots to do), Theatre of Magic (fast, fun), Bride of Pinbot (old-school but, again, I really like the layout), Medieval Madness (amusing audio, quite nice layout), Funhouse (although I found this really fucking difficult), and Monster Bash (really fluid and also amusing in how the story works).
I didn't really care for Black Hole (love the audio and general feel, but I don't like how it plays), Cirques Voltaire (just doesn't click), Gorgar (didn't really grab, although I now own it anyway, since it was an extra 50p when buying Monster Bash), Black Knight (I don't remember this at all!), and Creature from the Black Lagoon (found this a bit stomp your head into the ground).
Lots of great stuff here though, and I think the manner in which the testing has been designed is very smart. I'd have bought Theatre of Magic anyway, after what's been said in this thread, but in getting to fully play tables, really get into a game, and then get "OK, now buy it" when you're on a roll, that really encourages IAP. Compare that to Zen Pinball, which doesn't even show screen grabs of the other tables you can buy—madness. I wish FarSight Studios would sort out Retina issues on the new iPad though (either it's not Retina or there's an odd mix of assets) and rework the tedious, buggy front end. The app crashes far too often at that point but I've never had it crash in-game (as in, when playing a table).