Choose a race that will fit with the kind of character you will play, choose a khajitt if you're going to play a pure assassin, because they start out with sneak skills and their racial ability lets you see better in the dark. Choose an orc of you're going to play a berserker warrior, because they start out with warrior skills and their racial ability doubles your damage and halves your damage taken. What really counts is the racial ability (and resistances, e.g. nords are 50% resistant to cold, bretons are 25% resistant to magic damage, etc.), each race starts out with certain skills, but you can get those skills up even if you're a different race.