I definately think the FXO GTR suits my style the best, I've driven the other GTR cars, and I've become proficient (read, mediocre) with the FZ50 GTR, but I simply enjoy the FXR the most. I like the way it looks, sounds and drives.
I don't want to be forced to drive a car that I don't prefer simply because "That's what you need to do to win." Sure, that's the way it is now, and sure I can race with any of the GTR cars, but that doesn't mean it's right.
Also, as many have said, the FXO GTR is easiest to drive, I'll agree with that, in the sense that you're the least likely to simply lose the tail and spin out while racing, but I also think it's challenging and rewarding in it's own way. I don't think it should be slower just because you can correct slides easier than the other two cars. As has been said before, at the top levels, ease of driving means nothing, a good driver can be consistent no matter what car they are driving.
You can call me biased if you like, since I drive the FXR the majority of the time. I guess that is true, as I'd like to have more of a chance of winning with the car I currently enjoy. That being said, I have loads of fun with the GTR class as it is right now