Community Noise Maker
Sonic Team Junior
There's an argument to be made that the baseline itself needs to be adjusted, but that's a discussion all of its own.I like Sonic as a vanilla character that forces you to play the stage as intended. Tails, Knuckles, Metal Sonic, and Fang all have abilities that let them violate intended stage sequencing. A character who can't break sequence ever is a good baseline for both stage designers and players.
For custom level packs, I've considered locking all characters other than Sonic at the beginning of the game, so unlocking a new character provides a new-game-plus experience where you interact with a stage differently.