Tough, it's like asking a parent with 3 great kids which is their favorite. Do you have experience playing any of them? If you do and you enjoyed it, I'd suggest it.
All 3 are fantastic. You really can't lose here. MM is the shallowest of the 3, but it's the most approachable and family/guest friendly. It's a classic. The other two are in Stern's top 5 best games ever. Really you can't lose. You'll get them all eventually anyways, so just pick one.
I'm not sure anyone can honestly tell you a cutoff date for when you can never order them NIB, unfortunately. I do know Metallica's license was renewed at the end of last year, but no idea what that means in terms of how long they'll be available new.
I don't have any clue about the other two. I hope MMR is available NIB for another two years because that's how long I'll have to wait on that guy. Redoing the floors in my house instead of buying pins this/next year
Really difficult decision between MET & TWD Premium. Both Borg/Lyman masterpieces, and quite frankly, the only two Sterns in production that people should be considering for purchase right now. Both with unique gameplay & deep balanced complete coding.
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