My set up:
- Left stick to steer (see below for method)
- R2/L2 for throttle and brake respectively. To me this is so much more realistic than having them mapped to one stick, can you imagine if it was one pedal in "real life" you had to lift in order to brake? They are two different functions entirely and sometimes need to be used in unison.
- Right stick for gear up/down I think will suit me best, when I stop relying on AT (I know, I know) though perhaps R1/L1 is less prone to accidental shifts. I miss the "semi-automatic" gearbox from the previous games
- I strongly recommend grips for the sticks, and clip-on triggers that go on the R2/L2 buttons. The most popular brand is Gioteck (sp?) but in the UK there is a lesser known brand called Orb and they make tougher ones. I also use a silicone skin that covers the whole controller, which makes it grippier and a little larger to hold, which I picked up for £1 at Poundland =)
Personally I don't find there is enough travel in the stick to truly "steer", in other words I don't hold the stick under my thumb all of the time and tilt it. I do some of the time but for minor adjustments or straightening out I flick the stick or kinda tap-tap-tap on the side. For this I recommend the grip "caps" for the sticks that have the little bumps on. If you manage to steer with your thumb on the stick 100% of the time, firstly I take my hat off to you, then I would recommend the grips with the concave recess in the top, to rest your thumb in.
For some of the Nascar events where you have to stay between those cones, there is a method where you can push the stick fully forward (12 o'clock) then kinda grind it around to the left and right a little to steer, but this only works when you need very small and very precise steering inputs, else it's too hard to go full-lock. Works wonders for those challenges though.
I also tend to "pump" the gas and brake occasionally to prevent wheelspin, oversteer, lockups etc. though I keep ABS at 1.
When all is said and done, the DS3 is a pretty nifty controller but just does not have the travel/"play" in the sticks or buttons to provide a fully realistic experience, and whilst you can still put in quick laps (check the seasonal boards, plenty of DS3 users like Doodlemonopoly do very well) it's generally achieved in a much less smooth way. Tyre deg as a result also comes more swiftly.