I've always used a controller for racing games. Only recently did I pick up a wheel (cheap $30 Driving Force Wireless) and at first I just couldn't get used to it. I sucked so bad with the wheel I actually went back to the controller for a couple weeks after buying it. Went on complete most of A-Spec and Special/Seasonal events with it. But finally last week I forced myself to use the wheel again and I am proud to say I am now better with the wheel than the controller.
As far as I can tell there are two main reasons. First being the far more precise throttle and break control that the shoulder buttons of the DS3 could provide, and second the much higher precision that the wheel allows. Just finished golding all 3 sets of seasonal events as well as the B and A licences using it.
For people not wanting to invest in a DF GT because of the cost or space reasons I highly recommend the Driving Force Wireless, its cheap and just sits on your lap (I strap it to my legs using a belt, it does NOT move when you do that) and doesn't even come with peddles. It uses the paddle shifters as gas and break and it works great once you get used to it. It also works on the PS2 and PC which is an awesome bonus and a great way to experience gt 3 and 4 if you have yet to do so with a wheel.
Give it a try if you haven't, people aren't kidding that it adds an extra level of fun to the game if you take the time to get used to it.