What are some other good beginner bikes?
Once upon a time, bikes around 350-400cc were considered "nice middleweight" bikes. Later, 500 cc bikes took over that role. These days, magazines will call anything under 600cc a lightweight. This is not a progression which we think is particularly good. People who start out on an overpowered bike are more likely to get in trouble, will learn less, and may become so frustrated (or scared) that they give up the sport.
We don't necessarily think that the Ninja 250 is the best starter bike for everybody. There are good alternatives. For a lot of people, a Ninja 250 may be a better second bike. For those with no experience, getting some miles in on a lower-powered bike (such as a 4-stroke single) to get used to the basics of motorcycle control is a good idea, before getting on anything as serious as a Ninjette.
It's not only sportbikes that have gotten bigger in the past couple decades. Common wisdom these days says you have to have an R1200GS-sized bike for serious traveling, but there are many books and magazine articles about people riding to the back of beyond on 300cc-ish "scramblers". A 250cc thumper is still considered a big bike in much of the world; if folks can get from point A to point Z on one, then you can certainly use one to introduce yourself to motorcycling.
Here are some suggestions of bikes you should consider starting on. Get on the internet and do your research. You should be able to find something to suit you. Keep in mind that buying used is often your best bet, especially on a first bike.
To give you a basis of comparison, Kawasaki's advertised horsepower rating for the Ninja 250 is 33 or 36. Assume most manufacturers will fudge about the same amount. And remember that more is not always better.
Dualsports & Motards
Small dual purpose bikes are great beginner bikes. They're very light and, since they're also meant to be dirt-friendly, tend to have very forgiving throttle characteristics. They're also generally designed not to break anything very expensive if they fall over.
One thing to keep in mind is that dualsports and motards are, by definition, on the tall side. They are street-legal off-road designs, and as such need a lot of suspension travel and ground clearance. If this is a concern of yours, look at the seat height specification on the manufacturers' sites, sit on one for a while, or deal with it. For comparison, the seat height of the Ninja 250F (88-07) is 29.5 inches.
These dualsports aren't quite as tall as some:
One of our fellow 250 riders says: I think most people should start on a scooter, then hop to a bike. It really helped me out. Riding a scooter made the jump to a motorcycle a lot less intimidating. The first time I sat on my 250 it did not feel foreign or intimidating. There was a lot of learning, obviously, but since I already had experience on a 2-wheeled vehicle, it was a natural feel.
So yes, we do recommend scooters. They will help you get out on the road, learn how to handle a bike, behave in traffic, and enjoy the 2-wheel experience. They are very low maintenance; with belt drive and automatic transmissions there is very little to keep an eye on, which gives you more time to enjoy riding (but make sure to keep up with the service schedule).
In general, Honda and the Taiwanese brands (Yamaha, SYM, Kymco) have a lot more experience than any of the Chinese names you've never heard of. Paying a little more for quality can actually be cheaper.
There are some major differences between scooters and real motorcycles that you should be aware of. None of these are bad by themselves, but they can make transitioning to a motorcycle a little difficult.
While there may be a lot of 50cc scooters on offer right now, try to ride one before you commit to buying. New riders may not want to fuss with the extra oil maintenance needed on 2-strokes, and you may find that 4-stroke 50s don't have enough power, depending on where you live and what your intended use is.
Many people find 50cc scoots barely adequate in most areas, unless it's really, really flat with no traffic. Most 50s will max out at about 35-40 mph, which means you will have someone breathing down your neck a lot of the time. Urban-only settings may be OK, if speeds are slow and trips short, but you are most likely going to be better off on a 125 or larger, even as a beginner.
There are few things in life as fun and fulfilling as motorcycling. So, go find yourself a good bike to learn on and join the cool kids.