I just sold my JP2 Pro after picking up a STh Pro. For me, STh code is more accessible, and it can be a real flow monster like Iron Man. JP2 has a lot of satisfying shots too, but they’re much tighter (that very cool shot geometry comes at a price). I found the paddocks got repetitive after having the game for a year, and it was too hard to get to the Wizard modes (in fact, I never saw them). JP2’s art is a 9, where STh is more like a 6. But I like the mood and music of STh much better than JP2. And the UV lighting is a stunning effect, with the hidden playfield art coming to life.

All of the games you listed are great, just very different from each other. Pick the theme that grabs you the most, or do what I did and play them all a bunch of times.

It looks simple, but the 4 drop targets and the kickout from the left saucer really make the game. And the left orbit shot up the right ramp feels great.
You don’t get tired of the Demogorgon because each DG mode is different, and earning it gets progressively harder.

I think your main issue with STh Premium is going to be finding one. They’re scarce as hen’s teeth.