For me it’s Jurassic Park. It’s approachable by casual players who can just go for things like T Rex modes or raptor multiball but has depth to the point I don’t think I will ever see everything in one game. Some games I try to get through the paddocks others I concentrate on multiballs, others I try just for score or to get to a mini wizard mode.
After watching some streams of Avengers Infinity Quest I feel like that one could be as good but would need to play and watch the code develop it to find out.
I think I’ve played all the Spike 2 games a good amount except EHOH, haven’t played that one or really watched much video so I can’t speak to it but I hear good things.