I finally did get to playing some of the classics last year, excluding Sonic CD since that's a bit harder to find. I definitely want Chemical Plant Zone, it was my favorite level in Sonic 2. I'm not a fan of Oil Ocean Zone, though. It could look great in HD, but I thought it had some of the cheapest enemy placement in the game, excluding Metropolis Zone. But then again, these levels are being redesigned... It's kind of hard to think of what stages will be included, because some of the most popular ones have similar themes to each other, but it might be better to go with as many diverse looking environments as possible.