What kind of dirt bike should I buy?

It depends on what ya want to use the bike for as to what one you should get. You must know how to ride if you have had 4 bikes since 2001. If you are buying new then you can't go wrong really as all the brand name bikes are good and as long as you buy to suit the use then personally it is just up to you what one you want. I don't much like KTM bikes but heaps of people do and I know the crfr250r 2010 is a good bike but then so are the other brand 250f's like the Yammie and the kx. I would not really get a 2 stroke 250 unless you have a lot of experience as they are a lot to ride and the rider gets pretty tired in a race by the end racing one and they would not be all that good in the woods either. Maybe add what you want the bike for. Good luck anyway.