I too am looking at a 2012 Ninja 250. My plan is to keep it for a year or two at most. While I can't answer for the OP my reason for buying a new 250 is that I don't have to worry about "what is wrong with the used one". I am a noob to motorcycles and I really don't have any friends that ride so I can't bring an "expert" along with me to check out a used bike. Ninja 250s seem to hold their value, or at least I see that when looking through Kijiji and Autotrader. Most people have their 1 to 4 yr old 250s up for $4,000 to $5,000, I can get a new one close to the same price..... and its NEW. To me spending an extra $500-$1,000 for a new vs a used Ninja is worth it. I want to concentrate on learning to ride vs worrying what might be wrong with my first bike.
Having said all that my second bike will 99% be a used one.