He's likely chosen by now, but I'll still put my opinion here for anyone in the future.

For new tanks, I think PLD has some major advantages over the other two, specifically in dungeons.

Flash, Sentinel and Bulwark, and Hallowed Ground.

Run through a group of enemies -> Flash -> keep running. It's painless. DRK can do this with Unleash, but they have less mitigation.

Sentinel and Bulwark are excellent for new tanks who may not know what CD to use and when. Now we have several.

Hallowed Ground makes that-one-huge-pull-some-dungeons-have a walk in the park. Group enemies up, pop it, and spin. Once it's down, use Sentinel and dodge AoEs while spinning like a ballerina.

PLD seems to have a strangely high skill ceiling with Cover, Intervention, Divine Veil, and Passage of Arms. This might intimidate new tanks, but it shouldn't because we don't always use them.

Sword Oath + Cover the MT + a cooldown if you need it. Cover should be used sparingly in dungeons because you can find yourself chunked out of nowhere, and we want to avoid giving healers heart attacks.

In dungeons, Divine Veil can be used whenever -- I think of it and Intervention as bonuses.

PLD has a lot of extra stuff that can be useful, but most of the time won't be, which makes it easier to use than it might look at first.