I've decided to do some testing since the newest discovery in Pet Racer - 30 FPS strat.

I ran Low Gravity at least twice with every character (yes, I know Fair Play would be much better but I didn't think of that). Haven't tested using multiple pets on one run. These are the results:

Panther - 10:43 - best top speed, great if used well (@dootz_'s run)

Dinosaur - 11:06 - bad

Chicken - 10:52 - mid

Frog - 11:04 - meh

Tortoise - 11:09 - bad

Shark - 10:36 - good overall (improvable)

Bull - 10:15 - surprisingly good

Giraffe - 10:40 - mid

Bear - 10:17 - good

Gorilla - 10:21 - decent

Robot - 10:02 - great because of turning, my choice

Lion - 10:28 - mid

Conclusion: Panther is the best choice because you don't have to mess around in character selection menu, Dinosaur and Tortoise suck, unlockable characters are better than I thought, Robot slaaay.