For a beginner i would say a supermoto or dual sport is the best. A 250cc sport bike is pretty pointless and you won't want to start off on something a lot bigger than that. With supermotos and dual sports you can still have fun even if its not a really fast bike. Go off road jump curbs and...
My openion is to always buy used when it comes to stuff like that. You can save so much money just by getting something a year old. And you can find a lot of like new bikes with low miles on them for a fraction of the cost.