I'm sticking to Sonic 1, but with the caveat that its zones have appeared and been further developed in a few other games since 1991 and those other appearances are also fair game for grabbing stuff. So Green Hill Zone uses the caves and launch ramp from the GG version (although unfortunately I doubt there's enough sprite room for the giant fish from Sonic Generations), and Labyrinth Zone uses the mine cart and giant boulders from Sonic 4 Episode I. Which isn't to say that I might not grab obstacles from other zones entirely, but the environments themselves are all from Sonic 1.