My fav Sonic Char EASILY differs under what context, but all of the catagories answers change quite alot. But for what it is now;

Sonic; The best Char personality wise.

Knuckles; The best Char to play as.

Ray / Mighty; Vibe winners, and I bunched em together cuz they're a big duo, and it just kinda depends on how I'm feelin' most of the time it is Ray though

Overall; Ray or Sonic. Interchanges really.

here's an alt / outdated version for what it probably might(y)'ve been in the past;

Sonic; Best Char personality wise.

Tails; Best Char to play as.

Knuckles; General Vibe.

Overall Favourite; Knuckles.