Now I have a wheel.. but i can say Sixaxis is way more easy if you are used to it.. I had 95% of game completed, and alot very hard challanges with controller.. with wheel my lap times are slower.. since you have to drive the car.. and turn steering whee for real.. with sixaxis you can quickly change direction, and if you are used to it its more easy for sure.. but wheel is more fun and feels more natural, replays looks alot more real when driven with wheel (DFGT in my case) with sixaxis its jus very unnarual steering movements... Steering wheel is best, but hardest for sure (if you are used to sixaxis, if not then wheel will be more easy for you.. anyway I think its more easy to control the car with controller, esspecialy when you need to correct mistakes, it was very easy for me) with wheel its very different game.. I should say like with sixaxis its Need for Speed and with Wheel its rFactor... LOL something like that..
DFGT for racing
Sixaxis For drift and fast lap times in rally, and sometimes on regular tracks.
G27 for me I used to have a Driving Force EX which did its job well, but nothing compared to what a G27 can do.
I can't really imagine myself playing GT5 with the DS3 I strongly wish every single one of us GT lovers had a wheel so that those who don't have one could enjoy the game at its best