[SuperSonic94]

Sonic Adventure DX: Probably Casinopolis, Ice Cap or Final Egg

Casinopolis:

Using Sonic: Its possible to sub 7 seconds this level, but the glitch for that is hard...In this level there are a lot of walls that can be crossed...Doing the normal way its really hard to sub 2:30...Glitches ftw!

Using Tails: Going up at the start of the level, flying to cross the roof...I love that glitch (How do you think I got the World record for this level? :P)

Ice Cap:

Using Sonic: Very obvious...This level is a bit stupid, touching the first checkpoint, next to you there is the door to finish the act 1... Its really easy to cross that door...

That glitch to crossing the wall when the time is stopped is really easy for Gamecube version... In Dreamcast version its impossible to cross that wall, but there are a different wall to cross there...

Using Tails: Ramp trick...With the trick of some ramps you can go very far, using that two tricks correctly you save like 8 - 10 seconds...

Final Egg:

Using Sonic: This is one of the most large levels in SADX..., but not for Dreamcast version, since in this version you can sub 8 seconds because there is a capsule floating in the air, out of the level..

In Gamecube version, that capsule are not in the level, but there are some walls to cross to sub 55 seconds..When you go to act 3, just throwing to the left after going out of the elevator you can fall in the capsule...that is an important and quickly glitch in Gamecube version...

Now you decide at Sonic Adventure DX and Sonic Adventure 2: Battle.

[Jawzunx]

SADX (I will only comment levels you didn't):

You forgot about Lost World - Sonic:

In the big room with the snake you can get through the door which takes you to Act 2, so you don't need to activate the three switches.
Then, near the end in Knuckles' part of Lost World you can perform a gravity glitch by standing on a bright panel and then restarting, you'll start your next life in the last checkpoint you touched with the gravity altered. So far as I know this glitch can be used as a big shortcut only on the checkpoint before the rock.


Twinkle Park - Amy:

Right at the beginning of the Mirror Castle (Act 2) you can get through the corner of the main door and the wall. You skip big part of the castle by this way.
There is also a glitch not to save time, but for collecting rings. After exiting the castle there is a part (I don't remember exactly where) where you can jump through and fall onto the beginning of the stage where the pool is. You can get as many rings as you want by doing the stage once and again without thouching the baloon.


Some other glitchy levels are Hot Shelter with Amy and Gamma


SA2B:

Just watch SadisticMystic's videos.
Oh, and Sand Ocean has a 'freezing time' glitch as well.
Also City Escape... oops that's secret :)

[SuperSonic94]

Confirmed: SADX is definitely a "Glitched" game. :P

Ok, there is a ranking for the most glitched level. (Only using sonic)...

This is my opinion:

1. Final Egg: 9.50 points. Only for Dreamcast Version
2. Casinopolis: 9.00 points. The glitch for this level is awesome like the Final Egg glitch, but this level is a bit short than Final Egg
3. Ice Cap: 8.50 points Obviously... Stopped time, and those other shorcuts
4. Lost World: 7.75 points. Jawzun said everything. Doing a decent run, you can touch the first checkpoint at 20 seconds, at 31-35 seconds using some cool shortcuts you can arrive to the door quickly, and you can cross it spindashing a corner of the door, and that other shortcut of the "altered gravity".
5. Sky Deck: 6.00 points. All the shortcuts are good, but the shortcut of hitting the capsule before the gravity alters is amazing, doing the normal way, act 3 should be completed in 2-3 minutes. Doing all the shortcuts counting the capsule shortcut, act 3 should be easily completed in 10 or 15 seconds. Is impressive that difference of time.
6. Windy Valley: 5.50 points. This level is at 6° position because that big shortcut at Act 3, and for all the other shortcuts, all of them are not hard to do.
7. Twinkle Park: 5.00 points. Nothing much to say here, the big kart shortcut for Dreamcast (DarkSpinesSonic show us that its not impossible to do it on Gamecube), and avoiding to be raised to the kart starting act 2, spindashing so far you can arrive almost to the end of the level.
8. Speed Highway: 4.75 points. Cool shortcut at the start, you can save a lot of time, but the rest of the shortcuts are easy to do sub 1:20 minutes.
9. Red Mountain: 4.50 points. In this level there are a lot of shortcuts, but all are simple to sub 1:20 minutes the level. (Inclusively to sub 1:00 minute if you do all the most fast shortcuts correctly).
10. Emerald Coast: 4.00 points. Not hard and big shortcuts, but there are a lot of them on this level.