Are you talking about the kawa and yamaha or the ninjette and honda 250? Id go with the Honda since its updated with fuel injection, I like the instruments better, eides well at low and mid rpms(or so I hear). Don't know why kawasaki has not fuel injected the american ninjette when they do in Europe.
When I was searching around for one, I found that the yamaha and the Ninja 250's were both carb and i was OUT.... My first bike was a 97 ninja zx6, and was carb... I got it cheap and paid a ton to get it to where it was ride-able and i will do anything i can to avoid something with carburetors on it after that. they're high maintenance, and have performance issues after that.
Just one man's opinion, but I once had someone say 'anything to get that wind in your face is worth it'... motorcycles are awesome any way you cut it.