It depends on how strong the airbrakes are. By using L2 and R2, they have a wide range of motion, meaning that analog control is easier. Pressing halfway down on R2, is easier than halfway down on R1.

So if Sony Liverpool made the brakes so they have that much intricacy, I'll stick with L2 and R2 (though I'll probably look for those trigger add-on peices to make it like the 360s triggers).

But if pressing halfway doesn't make a big difference, I'll stick with L1 and R1 because they're easier to double tap.