Well they're all great bikes and pretty similar performance wise. When it comes to riding comfort, the CBR is the best followed by the GSXR and then the R6. Since the R6 is a pure racing-spec road legal bike, it's got a very aggressive riding position so it can be a little uncomfortable for long rides. So for the street the CBR or GSXR are the best.
Looks wise, CBR is the least attractive for me, it's styling has always been a little bland for my tastes. So for looks/styling i prefer the R6 & GSXR.
When it comes to the track, R6 is probably the best choice as it has insane top-end power. However that top-end power comes as a sacrifice to the low-end power band, where the GSXR & CBR are a bit better.
So it all comes down to personal preferences i guess. They're all great machines.