I am a new rider, took the motorcycle safety course and want to know what is my best option out of these two bikes. I don't want go beyond my skills but I don't want to outgrow the 250 too fast. Also i'm 5'9 210 if that matters.
In your case I would recommend the 500 ninja. It is not quite as sporty of a sport bike as the 600, meaning it will not launch you off the back of the seat in 2 seconds, but will have enough power to keep you happy for a few years.
500r for sure because it won't even take a week before the 250r is boring, the 500r would be your best bet because it would be a bit bigger and not feel so small under you and more like a scooter