The CSR Wheel is better in certain ways beyond the paddle shifters. The wheel rim weighs less, and therefore is capable of spinning faster, and is also capable of providing twitchier force feedback. It can change direction quicker. The electronics are apparently tweaked in subtle ways too, but I don't know the specifics. The biggest knock against the CSR Wheel is that the rim construction feels cheap. The seams are exposed, and if you're holding it outside of 9 and 3, you're just grabbing glossy plastic.
The GT3 RS Wheel feels much nicer in the hand, and really feels like something out of a road going car. The rim is fully wrapped in Alacantara, so screw holes and seams are covered. The rim is heavier, which can dampen some sensations, and it won't spin quite as fast as the CSR due to the weight.
The wheels are heavily related though, so they're very similar in operation. The CSR should objectively perform better, if that's your main goal, as long as you're not sensitive to some of the cost-cutting in the rim construction. To me the biggest reason to go with the GT3 RS is the CSR Elite Value Pack Edition, if you're willing to pony up a little more money. 60 EUR more than the CSR wheel, you're getting a GT3 RS and the CSR Elite Pedals, which seems like a pretty good deal. You'll wind up with a wheel close to the performance of the CSR, with pedals that are significantly better than the ones that come with the G25.
