The beginning stats of the skaters are all roughly the same, and they're all boosted in the same way through the run so no one is better or worse due to stats. Special tricks are what kind of matter: as guished said a front or backflip helps you gets points easier as they have a base of 4000 which multiplies with spins. I prefer Jamie because in addition to a front flip his special grind is arguably the easiest special input in the game (up up c-up), and you use special grinds in the run a lot for a slight boost in speed.

With 700 1-stock matches (mostly SD'ing) it took me about 2.5 hours to get Mewtwo. This was basically a meme run but it also unlocks Puff, Dr. Mario, Pichu, Falco, Marth, Young Link, and Ganondorf. What's left is adventure mode to get Luigi, classic mode with Marth to get Roy, and then 24 character target tests to get Game and Watch. Based on the records it should be feasible to get those 3 in less than 30 minutes, meaning while long the run could easily be less than 3 hours total. I need to learn the target test runs but I'm gonna try to do this for fun.