A large part of what I love about RPGs is trying new ones—not just new settings, but new mechanics. I love it when a game forces me to play in a different way than I ever had before, or comes up with a new way to describe characters. I play RPGs to have new experiences, and one of the ways I get those new experiences is with new games. So I don’t think there can be a “perfect game” for me—at best, it would be the “perfect game right now”.
That said, I can tell you the game that is my baseline. Whenever I’m getting ready to run or play a new game, whatever the game is, the question in my mind is “how is this game better than running the same premise/setting with Primetime Adventures?” I use Primetime Adventures the way a lot of people use GURPS or D20 System or Savage Worlds.
But even then, the answer is “it’s not”, and I therefore end up using Primetime Adventures, only probably one time in ten. So while PTA might be as close to a “perfect” RPG for me as anything, I don’t think there’s anything that really deserves that label.