As Gary says, London's Brunswick Centre has both JP2 Premium and GZ Pro. I played them on Friday, back-to-back, and would heartily recommend either of them - Keith Elwin is an exceptional designer.
I expected JP2 Premium to be definitively better, but the moving T-Rex head isn't as exciting as I expected. I hoped it would eat and throw the ball ALL THE TIME... and, sadly, it didn't. So, you're probably not missing too much with the Pro. Likewise, although the GZ Pro has some awful plastic standees (e.g. MechaGodzilla), there will be lots of after-market mods to replace it, I'm sure.
[Controversial opinion alert] The Brunswick Centre also has several other newish Sterns (e.g. Mando, LZ, Turtles, The Beatles, Stranger Things). I've also played Deadpool Pro at another London venue, Chief Coffee, and, personally, I don't think any of these are worth the money over famous older machines, e.g.
AFM, LoTR, FT, WH20, Ghostbusters, ST:TNG. I also quite like Avengers: Infinity Quest so, for me, personally, the appeal is Elwin as a designer [/end controversial opinion]
What I would say is that, despite being a rubbish pinball player, I prefer challenging machines like Total Nuclear Annihilation and (well-configured) Fish Tales. If you prefer an easier machine and are keen on a NIB, I'd maybe look at Mando or Deadpool instead - these seem to have a high rating among people who don't like a pin to kick their backside. If you're looking for a gentler play, I'd definitely recommend choosing your NIB by theme - rather than play style. Also, Stranger Things (specifically) plays almost exactly like
AFM/MM, which is why I don't like it - there are MMs/AFMs around London and I'd rather play them instead.