It really comes down to personal taste...they are all excellent, reliable machines...but different...and where the hell is KAWI!!!!
1. Honda - very reliable, very dependable, very compliant, very bland...i've had two (an F4 and a 1000RR) and loved them, but the Honda's seem to lack a little soul power
They are IMO the best all around machines...doing everything very well, but not really the best in any area...
2. Suzuki - never really my bag, i've never had one and can't attest to their quality personally, but they are probably the biggest player in the sportbike game and started it all with the GSXR-750.
3. Yamaha - seems to have "gotten it" with their marketing. Yamaha has focused a lot on looks and style in recent years...not to say the engines and performance aren't outstanding too...first gear tends to be a little tall and the R6/R1's don't have much of a low end grunt comparitively in my experience.
4. Kawasaki - bulletproof...IMO the most dependable engine in the market (knock on wood
) Kawi is known for big muscle.......and heavy bikes, but they seem to have rectified that witht the new ZX's....my favorite Japanese brand.