Depends on the game and how they use the controls. I adapt based on the control system of the game. For instance, racing games or shooters that use R2/L2 as triggers, I use index fingers.

Games like Metal Gear Solid where the R2/L2 buttons are used for weapon/item switching, I use both.

I can switch instantaneously without facing any discomfort. However if the game doesn't involve actions where I am forced to use both at the same time than I mostly use my index fingers. Racing games mostly with middle fingers though.

I only use my index fingers for the triggers and bumpers, unless I feel brave enough to claw on Halo...

I like using middle fingers with dualshock 3, however, 360's triggers are too thin to do this, so I have to change to my index fingertip.

depend on the game.
i remember guitar hero for ps2 and mario kart double dash for GC, i used to use middle finger.
all other, index.

Nintendo messed me up, now I don't know how to use anything but a remote controller.

I only use my index fingers most of the time. It just feels way more comfortable and I have a better grip on the controller.

You guys should try to get used to using middle fingers it really does make everything very easy once you learn to use them as well as your indexes.

It really depends on the game for me. Metal Gear Solid i use my middle finger, but other games i might use index

Only when I play Forza (completely manual).