OK, so Generations in on its way, and we know SEGA is going to include levels from his classic days all the way to his modern days. Green Hill is the only level that will apear in both console and handheld versions. We also know that City Escape and Rooftop Run will be in the Console version; also Casino Night will be a handheld-only.
Let's imagine the game will have one level per main console Sonic game. Which Zones/Stages from Sonic 2 (Not counting Casino Night), CD, 3, & Knux, Adventure, Heroes, Shadow, 06, 4 and Colo(u)rs are your favourites/do you want to be incuded?
Mine are: Chemical Plant, Stardust Speedway, Icecap, Flying Battery, Speed Highway, Rail Canyon, Lethal Highway, Crisis City, Splash Hill and Asteroid Coaster
EDIT: Please leave your lists of favourite levels from each game, so we can see the most common.