The Ninja 250R is very different from most of the other 250s like the Rebel and TU250X. The Rebel and TU250x and most other 250s are air cooled and very small. Great for the smaller rider but may be too small for longer legged. In addition the air cooled bikes have considerable less hp. They are fine on most roads but will struggle at highway speeds. The Ninja feels much bigger, is heavier and has 30-50% more hp. It is very capable at any legal speed limits.
I think the Ninja 250r makes a good starter bike for most riders, especially a used one. TU250x and Rebels are good for smaller riders as they are lighter and lower. Dual sports and supermotos are good for taller riders as these keep most of the advantages of the other 250 bikes but are less cramped.