Definitely DFGT. I just started playing F1 2012 as well with my G27. Had to adjust my pedals again so I will have a good spacing between the brake and the gas. Clutch and shifter is not needed since the wheel has the paddle shifter. If you can't afford G27, just go for DFGT.
There are other wheels such as the T500 and the Fanatec line, but Logitech in quality and customer service is just unbeatable. However, i'd wait for a replacement for G27, if there will be, if you plan to skip T5 and Fanatec.
Personally, I find the clutch useless since there are only few games out there that support a clutch. Even if they do, it is close to being useless.