Guardians don't put out quite as much dps as Sentinels do BUT they do have utility in ops that sents don't.
ie taunts, more defensive cd's ect. This being said both have uses in ops and pvp so ultimately the decision to make is more dps and 2 sabers compared to more survivability and 1 saber.
Playing both, I enjoy sent for dps but the guardian force push and guardian leap are so much fun lol