2. Bard is the most useful sub-class. You would have more damage if you went for ravager, but want do you want? Having decent damage and tankiness, therefore not being that important in groups, or go for what will make you invincible? Going bard would mean having nice flat heals and HoT, while having put your points into speed gives you reduced cooldowns. And if there is already a bard in your group, that won't mean you will become useless, it will actually make their job easier as they won't have to renew the HoT spell every 15 sec aswell as healing everybody with their 3 other heal spells. Also, healing generates menace, so you would take some off of them by healing too.
Actually bits of this are untrue. Bard sub is nice to keep yourself healed, but since bard main players will refresh HoT on the entire party, their going to refresh it on the tank regardless.
Also with the malicious passive and other passives on the new envoy path, most tanks can keep aggro later without even having to use taunt, so a healer stealing aggro off you is never an issue.
Also Ravager's AoE stun allows for the party to mass mob aggro a dungeon and then just stun and keep malice as the party safely chews away at a group, harp can do this as well as a sub.
Guardian/Bard is more PvE, while Guardian/Ravager is PvP, but Guardian/Ravager can also tank PvE perfectly fine if you know what your doing.