I've driven with the T500 and CSR Elite and prefer the G27. We've done back-to-back tests at work with real racers and they constantly perform best with the G27 and find it has the best "real world feel". Of course this is all subjective... But the biggest comment from drivers is the G27's FF algorithm provides the best tactile feedback, letting you know what the car is doing. The T500 is a close second, and the rim is a big improvement over the G27.
The G27 pedals, with the GTEye spring, are better than the T500 pedals. The T500 brake is really lacking, but can be improved substantially with BasherBoard's "even stiffer brake mod". Although, again the driver's feedback is the G27 brake with a GTEye spring gives the right feel and the sweet spot of the spring is excellent.
I've modded my G27 quite a bit, but can go almost as fast with the stock one at work (it only has the brake spring changed).