I always used the L2/R2 for brake/throttle. I did try the right stick a few times, thinking that I might have better control, but I was completely useless with it. From memory I think I'd generally use X and Square for gears. Makes more sense to me than having two fingers right next to each other on the same hand handling braking and downshifting in a braking zone.
I was a bit

at "d-pad for steering", but I suppose really... that's pretty much how I used the left stick. Too hard to make fine adjustments, so I was basically just slamming the stick one way or the other. Now that I think it about it, probably would have made just as much sense to use the d-pad.