first bike? wahts your weight/height? There is NOTHING wrong witht he 250 4 strokers, Im a 2 stroke guy, but the technology and the R&D are soooo good in the 4 strokes now that they ARE the bikes to beat on the track. Take a look at ANY motocross race and count how many 2 strokers you see out there not gonna be too many, the 4 strokes offer ease of riding as you dont have to be 'on the pipe' all th time to make any power. The ONLY downside to 4 strokes now is the fact when something in the engine goes kaplunk, your automatically out about $500, a 2 stroke can be rebuilt with a piston and rings for about $100, and since there is no camshafts or valves, the likelyhood of things breaking is slimmer, BUT, that is worst case scenario shit, id DEF recommend the 4 strokes ESPECIALLY for cruising in the woods and farting around in this florida sand, you'll LOVE the feeling of TORQUE

Other than that, stick with the 'big 4' and you won't have ANY issues, pick up a motocross magazine at the grocery store and read the reviews on each bike your looking at, they test them all the time and give ride reports. See which one they write about gets you a big grin on your face when you think about riding it haha

as for BUYING a dirtbike, if you are comfortable buying used, you can save thousands, an older YZF or CRF or the like will run you like $3k or less, but go and buy it new and your looking at dishing out at least $6k or MORE, yikes!