If you're too lazy to mix gas, don't buy a dirt bike lol. 4 strokes cost a ton more to maintain. You're a little heavy for a 250f, so you'd be winding it out all the time. And actually, 4-strokes aren't meant to be lugged around, and you'll hit the rev limiter sooner on a 2-stroke than you will on a 4-stroke.
Now, if you're dead-set on a 4-stroke, get a 450f. Sure, you'll never use all the power it has unless your last name is Stewart and your friends call you Bubba. But 450's don't need to be wrung out as much as 250's, so it'll mean less time between valve adjustments/ oil changes/catastrophic failures.
My personal suggestion is a 250 2-stroke. You can get a used one of cheap, they're cheap to maintain, don't have to worry about all that valve/cam mumbo-jumbo. Only downside is you'll likely get face cramps from excessive smiling.
If you get a non-motocross (like a yama wr) then maintenance won't be as bad. But a 2-stroke would do fine in the woods and you could hit the track whenever too.
p.s. I ride a 2-stroke and always will