Best breed of horse for experienced rider?

I have a really slow horse. She's so slow that her regular walk is like a western pleasure walk and the fastest she'll go normally is a medium canter. She's an amazing beginner horse, but she's basically the definition of slow, so I'd really like to get a new one in the spring. I really like Arabians but I've heard something about that since they originated in the desert, their skin is thin to let heat out easily and therefore are harder to take care of in the winter.
Anyway, I would like to have a breed of horse that is spunky, smart, no bigger than 15.2 hands, likes to run, and is a fairly easy keeper, and one that isn't a beginner horse. I don't really care if it's full blooded or a mix. Thanks for any answers!!