What characters do people use for time trials? Does it ever change depending on the level?

We would recommend starting off with Sarah. You'll find she has the best turning by far. Most of the tracks you are limited on trying to land as soon as possible and carry as much momentum through corners so Sarah will be your fastest choice. On some of the more open outdoors tracks her lack of turbo may not make her the best choice, but little testing has been on towards that.

Yeah I think I mostly used Sarah when I played, I was good enough to unlock the hill climb and everything else and get a win on every track on the hardest difficulty but I was thinking people might use Nigel or Bobby for time trials much like the Dave Mariner (Wavy Davy) of Wave Race.