Start at the nose and work your way back. Does he have enough extension through his front end, his he clean enough, do his shoulders set right or his he too straight, does he toe out, is he wide between his front legs, does he have a strong level top or does he break in it, does he have adequate bone, how is his tailhead set, is he deep enough, does he have enough muscle, is he wide set at his pins, and is he level from hooks to pins, does he set right on his back legs or is he post legged, does he have plenty natural spring of rib or is he a little flatter made, does he cover his tracks when he walks.
Those are all questions you should ask yourself. Most importantly though, does he put it all together in a nice complete package? As far as disposition goes, only you can judge that. I'm 6' 220lbs. so if I can't handle a calf or get it broke it's going to the sale barn, on the other hand though my little sister is 100lbs soaking wet and has only shown for two years so there are a lot of calves I wouldn't have a problem with that I wouldn't let her touch. A few things to look for are does the calf turn & burn from a quick movement or does it just kind of jump back, but keep watching you because it's never been around people before? The curious ones seem to be easier to work with. The ones that always have their guard up are the ones that will probably give you the most trouble though.