it really depends on what kind of riding you want to do... decide what kind of bike you want eg. trials, dj, freeride, dh.. etc. then goto your lbs and see if they got the type of bike you want and if you got lots to choose from, try them out and see which you feel is most comfortable. buy a size so that when the seat post is at its maximum lowest, you can have both your feet flat without having your legs straight.