I voted only classic haha. The problem I have with the adventure sonic and the 2000s in general has been mentioned by others. Sonic turns into a generic do-gooder hero type and his general attitude is largely transferred into Shadows character. Half the reason I liked Sonic as a kid was because of his impatience (and he was a slight a$$hole), it made him do cool stuff without being a try hard and acting cool, like he's trying to convince us constantly in the post classic era. Sonic is just dull here in general though, too many characters get shine and the stories aren't focused enough as a result. The problem I have with the modern era is that the rest of the cast is useless and tails in particular is annoying. He was somewhat annoying in the classic era but only in the cute little brother type that gets on your nerves sort of way. In the modern games he's just cringey. Knuckles is also dumb and in the classic era I never got the impression he was stupid, just naive because he didn't have interactions with other people often. In fact in sonic 3, knuckles outwitted Sonic virtually the entire campaign until the end. I pretend the dark age doesn't exist.