If you like adjusting valves every 10 hours and changing oil after every weekend of riding. Go for the CRF. If you want to have a bike that you just have to change the oil on once a month and stick a ring in once a year and piston every other year get a two stroke. Your size and weight I'd get a KDX 200 or 220 they're smooth and can be made as fast as you want it to be short of an MX bike.
I wouldn't rule out KTM's 300 its legendary and bullet proof. I would also look into KTM 200 its in the price range you want. I would also look into the Yamaha WRF's 250 they don't have the valve issues.
Right up front, I'm biased to two strokes because I'd rather ride than spend the weekend trying to retune the thing, over all its cheaper to own a two stroke. Look at it this way.
2 Strokes, you have 3 moving parts. Piston, Rod, Crank. 4 Stroke, dozens of moving parts. Crank, rod, piston, timing chain, cam, rockers x 4? valves x4.