Windy Valley- I'm not sure about this one. It's easier on GameCube, at least, but I'm not saying too much, yet. Muhahaha!
Casinopolis- I got about 18 seconds with ekgnew's improvement, and I think 15 is possible. 12 isn't, so far.
Ice Cap- I say they're exactly the same. I remember falling out of the tunnel being just as easy
on Dreamcast, but I guess that's because I dash against the boulder clogging the tunnel.
Jumping through the door in area 2? I don't know. F-Man thinks it's easier on DC. I didn't notice.
Windy Valley (Tails)- GameCube draw distance: really bad, and with overlapping glitches that make it look even worse.
Dreamcast draw distance: really, really bad, with pop-up like 50 feet away. :(
Twinkle Park (Amy)- I don't know what this is about jumping over the castle.
I guess the doors aren't "sticky" on DC. Anyway, I would think it helps, but F-Man uses the other shortcut.
Emerald Coast (Gamma)- There are more robots on DC. robots=time=win
Hot Shelter (Gamma)-
from my guide:
"<3. Freeze time and go through the Hot Shelter repeatedly.> (GC:yes, DC:no)
At the end of the stage, instead of falling into E-105 Zeta's area, jump forward and land at Amy's goal.
Go to the end of the platform and stop in the doorway. Jump out there and turn right. If you hover straight
out there, you should be able to get through the walls of a red, cylinder-shaped room and land on
the button that changes the path of the bridge. Because time stopped before you went into Zeta's room,
you can explore the level as much as you want."
But SadisticMystic said something about getting 128 minutes on DC, so that would give it the advantage.