Shoot the one that looks big.  OK, so that's only half silly.  Before going hunting, look at a lot of bucks (magazines, books, taxidermy shops, videos & TV, while scouting if you can) & get a feel for what makes up a handsome animal.  Scouting gives you a feel for the representative size of buck to expect in your area.  There's lots of "tricks" like comparing horn lengh to ear length (2 x ear length = 14 "), Prongs starting above the ears, etc. but for a quick assessment look for overall mass, height of & length of prong, total length & most importantly one that looks good to you.  If facing me, I like to imagine his face (nose to ears) inside his horns.  If it looks like there's not much room for his head in the horns save him for the last day.  If it looks like theres plenty of room to spare start thinking about trigger control.  Small bucks are obvious.  Nice bucks are REAL hard to evaluate & the big boys?  You'll know it when you see him.  Antelope are arguably the prettiest critter out there and any buck pushing 14 or more inches will make a beautiful mount to be proud of.