You’ll probably outgrow a 250, you may outgrow the 500. I would say get the ’07 ninja 250 since given that you might outgrow either the 250 or 500 and upgrade anyway, might as well learn the coordination on the easier of the 2. Of course, you should probably take my suggestion with a grain of salt since I started on an sv650s.
If there’s anything more important than my ego
around, I want it caught and shot now…