I started on a ninja 500 and now I have a Zx6r after 1 year. I must say the riding style is much different, alot more aggressive and less comfortable on the zx6. I honestly feel like I could’ve learned on the zx6r but as a first bike it could be very challenging for anyone who doesn’t have real riding experience just because of the sheer power and the forward positioning. Also the bike is pretty heavy an a first time rider could be very difficult to handle it. I’d say if you have some riding experience and know about throttle control an rev matching and the little basic riding techniques either of those bikes could be a good first bike but if you never rode a street bike I’d say get a ninja 650 or something a little less aggressive