I'm currently going through every mainline Sonic game in order of release date and ranking them as I go along. Currently, I'd say Sonic Adventure 2 is my favourite. The game has a lot of charm to it, from the updated models to the fantastic soundtrack. The way they organized this game feels a lot better than Sonic Adventure. Having the story go from the three characters in each side gives it a better transition and all the playable characters are fun. The only issue I have is how clunky the game feels at times. This is specifically with Tails/Eggman levels. The way the mech turns around can screw you over during some of the platforming sections, like with Hidden Base. If I had to rank every character from their levels, it would be:
1. Sonic
2. Shadow
3. Rouge
4. Knuckles
5. Eggman
6. Tails
I have to say though, Sonic and Shadow are close to being a tie, Knuckles and Rouge are also interchangable. I think that's a positive though, almost every level is really well made. I only have a few levels I don't like (it's mostly the desert levels except Sonic's) but the rest are really fun to play. Overall, this game was a lot of fun and I'm glad I enjoyed it more upon replaying years later.