if saving time is really what you want, as in getting groups faster and gearing up faster, go heals. the game is currently starved for them. If you want the fastest thing going, go augmentation evoker.
if you are starting a tank from scratch or are going to boost one, check out Izen’s youtube channel. he goes over the popularity of each class in the game weekly.
If you are on the fence about tank/dps, or even heals, paladin might be a good choice. they are very solid tanks as prot (great crowd control and support, but damage is a little light - pun intended), ret is decent dps, and holy are the top heals.
if you head down the tanking route, check out my post.