Leveling a tank is far from slow, it's just the opposite. Dungeon ques are always fast for tanks as less people want to play them. Tanks come in two flavors in this game: Paladin is all about mitigating as much damage as possible while Warrior is about having tons of HP, abilities that offer some self healing, and dishing out some damage in return. Paladin is the easier one to play, where as Warrior takes more nuance, therefore has more margin for error.

The great thing is you can try both and see which one you like better. Just know that neither really come into their own until after 40 (you could argue 30 for Warrior), and then again at 50.