What stroke is better for a dirt bike?

Um there is no "power band" on a four stroke so your logic is flawed. I will make it simple though. If you are 14 you got some growing to do so think big (and I mean cc's to accomodate how much you will think you will still grow (only you can guess this by family history size, etc and forget riding ability since you will adapt to whatever you decide on)). I personally hate four strokes (I have a 2007 Honda CRF450F and a CR125R) and can barely lift the bloated 450 on a stand (important when you are dog tired anyway from riding and drop it and then have to try to pick it up and start (eh another negative to four strokes)). It's a bloated overweight HOG. Four strokes are here for ONE reason only. The AMA rulebook (it would take me volumes to explain and involves politics and EPA emissions so forget that). If you are mostly planning on "messing around on the track" fine if you don't mind the weight, HUGE added expense (blow a four stroke engine (and you will) you are looking at 2,000 plus and a two stroke at most 300 and can fix with a butterknife). FOR NOW. MY ADVICE. Buy a good used two stroke (2006 but no earlier since most manufactuers haven't changed anything of relevance up to this point). Gear it properly, a good aftermarket pipe, DO THE PROPER MAINTENANCE and you can't go wrong? Wanna buy a 2007 Honda CRF450R pig? LOL

4 strokes have come a long way... they are the main staple in racing today... it is almost as if they have in a sense "outlawed" them because of EPA reasons, etc. If you are thinking an older model-and you are going to be doing a lot of trail riding and not balls out racing- I would definitely say a 4 stroke...on the other hand if you are going to be hitting the track and you are looking for something older, a 2 stroke would suffice. If you have a decent amount of cash to spend, a newer model 4 stroke can be raced or trail ridden.