I believe most/all of the Japanese manufacturers have a cruiser in the 500-650cc range.
Sportsters have the advantage of a low seat and reasonable power (similar to a 650 sport twin) but they are heavy for a beginner. A sportster weighs around 550lb while something like a Ninja 500 is 400lb, and a 250r is about 350lb. This means slow speed handling can be a challenge to learn and little mistakes can result in a drop where a lighter bike you can recover.
If you are a large strong person then that may work for you. Myself i would rather get a good used smaller bike to learn on then when I have more confidence buy what I really want. I think I will know much better after riding a bike for 5 or 10 thousand miles what I want in a bike than I do right now.
Craig