Using L2/R2 for brakes/gas gives you the most modulation and control. Definitely an advantage over using buttons because you cant consistently give detailed input on throttle range with shallow buttons. I personally use triangle for upshift because its the closest to your thumb when your index fingers are glued to the triggers. Then I use square for downshift. Left stick for steering as usual. Used to be stubbornly old school from gt1-6 and refused to use the triggers for gas/brake; just too accustomed to X/square that I couldnt switch yet at the time. Muscle memory is difficult to change but the ds4’s L2/R2 is an obvious upgrade because it has more range than previous controllers and that was hard for me to ignore. The long layoff for gt and surprisingly ALOT of gametime on gta online helped me make the switch and x/square simply cant match the triggers in any aspect once your muscle memory is reset.