Neither really require to much skill to use. Using effectively is different; people that mainhand shotties usually suffer from a lower K/D than others who can effectively shuffle their primary and special weapon, and can make accurate calls as to what the best approach for an engagement is. I feel sniping is simply too forgiving. The fire rate on even the high impact snipers is high enough to recover from a missed shot, and they even perform well when under fire. You do have to actually aim snipers, though.