I got into TPA first, because at that time I really didn´t like the "fantasy" style tables on Zen Pinball / PFX.
However, Zen Pinball is just much better made AS A GAME. Being able to save progress mid-game on my Vita and being able to use the face buttons for flippers instead of the shitty shoulder buttons like in TPA are two big ones for me.
The Zen tables are also more consistent physics-wise. Yeah, they might not be very realistic, but neither is TPA - and to be honest, I´m having more fun with most Zen tables since the physics are very forgiving and reliable, so I can contentrate on the table itself. On TPA I actually prefer the older and more brutal tables, like Firepower or Flight 2000.
The physics in TPA are simply all over the place. I enjoy them in Attack From Mars, where they feel precise and fast, but on other tables like Cirqus Voltaire the ball just moved like it´s made of styrofoam, not to mention the hungry outlanes that seem to magically suck the ball in. A guy on the Pinball Arcade Fans podcast said that Twilight Zone feels like an entirely different game compared to the TPA rendition, because the real one is much harder and quicker.
Zen simply doesn´t have that problem because it´s meant to be a videogame from beginning to end. They also really got a lot better - the early tables were kinda sucky imho, but Moon Knight, Infinity Gauntlet or Fear Itself are brilliant design and feel pinbally enough to not completely break my immersion.
Oh, and man, the sound effects in TPA are SO WEAK. The flippers sound like pretzels snapping in half, whereas Zen has samples that actually sound like proper coils being banged.
I feel that the good parts about TPA - the table design, my favourites being White Water, Whirlwind, Cactus Canyon, Attack From Mars and Creature From The Black Lagoon - have actually nothing to do with Farsight, since they didn´t design these games. It´s simulating awesome machines in a rather shoddy way.
And I say this as someone who used to really love TPA, but I find it very hard to go back coming from both better GAMES (Zen Pinball) and better simulations (Visual Pinball - which is a nightmare to set up, but once you get Road Show or Addams Family running, it´s so worth it).
To end the rant on a positive note: At least they had the guts to actually make such a product, licensing these machine must take a ton of work and I think it´s great that people can enjoy these pinball designs on such a huge variety of devices. Without TPA, I would probably have never discovered this brilliant genre of games.
I also feel that the team at Farsight are really nice people, giving interviews and having regular contact with people on the forums. My impressions are also mostly coming from the Android version - which has a particularly nasty audio delay bug, where every sound effect gets played a half second to late, which is very confusing and breaks the atmosphere a lot.