What size Ninja for a new rider?

There are two words you never want to hear yourself say on a motorcycle: "oh sh*t". You are much more likely to utter that magic phrase on a 600cc or 650cc than a 250cc.

The 250 *IS* midrange in speed and economy. The lowrange would be a SYM Wolf. The 250 is quite quicker than any cage. The only reason to get bigger is because you want to race and speed and other stupid stuff. If you want "Stylish" why are you asking about Fugly "sport" bikes? Get a crusier, customize to your personality... bagger, bobber, tourer, or even leave it stock.

250

How would a new rider know what quick is, let alone how to tell that a bike isn't? And you don't have to get a bigger one later. That's a whole new decision ....that comes later. A "responsible rider" is proven, not declared beforehand. If you really did understand the reasons behind the recommendation, this question wouldn't exist. I have heard it said that motorcycles are not like shoes that can be grown into. There are those that would still argue that. For them I offer this: If you were to wear shoes way too large for your feet, you would trip and fall on your face if you tried to run. Substitute motorcycle for shoes and skill for feet - same thing. You still have choices, though. The Ninja is not the only thing out there. Get the licensing thing out of the way, and then go shop. Sit on what you can, see how it fits/feels. Stay smaller powerwise, a beginner does not need the surprises that come with excess power. Most twins are tractable. Stay away from peaky in-line fours. When you find what fits, try to buy used instead of new. The savings works in a number of ways.

Next time you visit a Kawasaki dealership, ask what it's going to cost you to replace all the plastic fairings on a new Ninja. That's what you can expect to do sometime within the first year of riding any motorcycle, because it's a 99% probability that you will drop the bike at least once while you are learning to ride. If you buy a used bike, without all the excess plastic trim, it will be cheaper to maintain and cheaper to repair. A Cruiser style bike, like something in the Honda Shadow series would be easier and cheaper to maintain, and a lot more comfortable to ride.