Ninja 250 vs Ninja 500 which is best for a new biker?

well one thing you can do is buy the 250 used and sell it again when you are bored with it at the same price you bought it and then move on to the 500. just dont buy anything new until you have a few years under your belt. in that short period of time you shouldn't really do anything to decrease the value of the bike. Just remember the odds are very high that you will drop the bike. no matter how experienced you are you can get distracted enough to drop the bike at a red light. back when I was in MSF my instructor told us even after 22 years of riding. one thing I recommend is to put frame sliders on the bike to keep from damaging the extremely expensive fairings. good luck!