Quoted from yancy:

I've owned Maiden & JP since each was newly released, love both, never selling either. So I speak with love for both of them, but no jilted ex-owner bias.

Jurassic Park, hands down. Maiden is an all-time great game, but I wouldn't say it's especially deep, by modern standards. Fun every time you walk up to it, but from a rules standpoint you'll probably have a similar experience most times you play, unless you're a good enough player to occasionally reach Number of the Beast.
JP is like 3D chess. I can play it five times in a row and have five totally different games depending on where I focus my progress. There are two different mode groups/ladders, plus the dino paddocks (think MM castles, except you have to chase them around the playfield), three strikingly different main multiballs, more mini wizard modes than you can shake a stick at, fossils to collect, the constant stress of rescues, perks dependent on which island path you choose, and overall what I would call a very "textural" style of gameplay where the individual choices you make weave together to create countless different combinations.
It's hard for me to imagine a more rewarding pinball experience. JP has all the story/progress depth of a game like LOTR, with the blow-it-up score potential we've grown to love in modern games. Anything can pay off huge or be a total bust. There are no gimme score strategies. You'll earn everything, and love it.