Of all the 250 2 smokes the YZ is the most "well-rounded" of them all. The motor is awesome stock it pulls from right off idle and has power everywhere. I ride mine mostly in the tight rocky, snotty trails of western washington I rarely use the clutch and the bike can literally be ridden a gear higher than any of my freinds 2 smokes. The bike also sees regular track time and sand dune use. On the track just getting on a YZ will make you a faster rider, they are that good (and yes I have ridden most of the compettition). The only complaint is a little harshness from the fork. Other than that go get a YZ, ride it, and love it! O yea, i'm 5' 9" 165 lbs. if that helps.
I just got an '03 about a month ago. I also have an '03 KTM 250exc. I just got into Dirt Biking this year. The KTM is for racing Hare Scrambles. However the YZ is so great it might take over that spot.
I ride the YZ on the track and have ridden a few trails it rocks on both. Just look at Barry Hawk kicking butt in the GNCC on a YZ 250!!
You can save some $$ by getting an '03 if you can find one. The '04 is not much different. Some improvements that would be nice to have namely the forks. Otherwise exact same engine.