I currently have both an Yamaha XS400 and a Kawi KZ400. They are both single cam bikes from the mid seventies, and for grins I rode them back to back. Here is a little break down of their respective performances.
The KZ400 motor seems to be lacking power in the lower RPM range but then screams flat out up top. The XS400 is quite the opposite and is very torquey and quick off the bottom but loses steam once the speeds go up. Neither bike has a good performing front brake, but no brakes excelled in the 70’s. The XS400 feels lighter and is certainly more nimble than the KZ but does not feel as stable at high cruising speeds as the KZ does. Asthetically both bikes look fairly similar, the XS is a bit more linear where-as the KZ has more rounded edges. The KZ is built for a very short rider and has a lower seat height and closer pegs and controls, the XS is a bit more spacious (but not necessarily more comfortable). All in all the KZ seems to lend itself more to cruising and travelling, and the XS seems like it was built more directed at zipping around town and running errands.
If I had to ride only one I think I would lean towards the XS soley for the reason that it is a bit more roomy and I am a tall rider. If the KZ had its pegs lowered and short handlebars were put on it I’d imagine this would change my mind.