Honda, hands down the best bang for your buck, reliable, and parts are the cheapest.
If you are a really good rider (I don't think you are or you would know this) Suzukis have the best performance, but it takes a hell of a rider to get past what the Hondas can do. and even at that it's an inch of difference over a mile of performance, they are extremely close.
Yamaha just looks the best and is on par for performance with the other sports bikes, but I'm guessing (hoping) your getting a 600cc, and the new 600's don't come with the cool headlights so it's not really worth it.
Basically just go and see what is most comfortable and looks best to you, for me it was Suzuki, for you it's probably something else, just stay away from Kawasaki and know that honda is just slightly more reliable than the rest.