Smart Choices from the Start

Whenever you go for a Time Stat here on the site, I strongly recommend that you choose a rival (not your character) who will not attack you and impede your progress significantly. More specifically, Knuckles and Silver. However, I find that facing against Knuckles can be promising as well since he is kinda slow, seemingly, unless he gets his Special Attack.

For your actual character, don't use Knuckles; that I am sure of. Metal Sonic, Sonic or Shadow are good choices. If you choose Metal Sonic, though, be careful of which rival you choose as his special ability is the ability of your rival.