If you really want a motocross bike, not a woods bike, then any of the 250F models would work. The CRF250X that John mentioned is a great idea although it isn’t an actual motocross bike. It is very close to the R version though. I also like the KTM XCW line, but it’s up to you whether you prefer 2 stroke or 4 stroke. read more
The KDX200 is an awesome woods bike. Keep it as long as it makes you happy. I sold mine a few years ago to buy a KTM 200XC.I followed popular internet opinion to go for an XC model. read more