my honest opinion
flip a coin for it
they are both good games, starcraft is just arguably harder to get into. its harder to pick up, and the campaign is harder.
warcraft isn't too hard to get into, and the campaign actually teeters towards the easier end of the spectrum, save for a few missions.
but it mainly boils down to
-do you like a more macro oriented game where losing a few units isn't going to kill you
pick starcraft
-do you like a more micro oriented game, where every unit counts
pick warcraft
of course both games rely on both macro and micro, but generally starcraft is "HUEG ARMY vs HUEG ARMY" and warcraft is "SMALL SKIRMISHES" not to mention, talking both games at pro level here(hell, maby even at novice level), warcraft requires less apm(actions per minute) to be good at.