I think it depends for what purpose the game is better.
RC1: long time Mulitplayer Gameplay
RC2: playthrough fun with different modes
Actually i like RC2 a bit more, because i didnt had rc1 as kid (no nostalgia) and i had no intention to play either on multiplayer.
Both have their cons and pros. Physiks-wise i didn liked the aspect of both: "touch something and you spin-out" (it feels like driving a toy car) and RC1 has some really weird landing physik (i hate Daytona cause of it, landing on the "bad"-side of the car is a poker game whether you are allowed to win the race or crash befor the finish... i didnt played it to often but its like a 50/50 chance)
Music is great on both games. Items RC2 has some cool addtion but the wormholes ruins it. I liked the car design more on rc2, but balance is off. rc1 is better balanced. Against "Stage III"s opinion, i liked the RC2 camera, when you crash, more, because in rc1 the camera zoomed in on the car, so i just saw a big car with a small spinning background and after that i didnt know in which direction in need to go. (especially in tunnels) However, both camera solutions arent the best.
Tracks: RC2 has some better usage of the flipp-over/driving on the ceiling mechanic, but the tracks where all pretty similar. RC1 has more variety.
Also scramble mode from RC2 is pretty fun.
Everything thing said is just a opinion
there is no actual best.