Honda CRF450X, Yamaha WR450F, KTM 450 EXC, Husaberg FE450, Husqvarna TE510, Beta TT450, Kawasaki KX450F will be good for MX tracks and trails.
I know there is too much bike here, but the best for MX track in stock form is CRF I think, but WR is pretty good too. KTM 450 EXC feels very light and perfect for trails, not that much for MX track. You have to define your expectations in your mind, and then pick a color..
IMO, if MX track is not important, KTM EXC series will be perfect..