Since a single character can be every job in the game, that is in effect, the skill trees that you want.

Tank spec with lots of defensive cooldowns - Paladin.
Tank spec that's heavy on dps - Warrior.
Tank spec that's in the middle - Dark Knight.

Melee dps that just hammers and does massive damage - Monk
Melee dps with alot of utility - Ninja
Melee dps in the middle - Dragoon

Healer with strong single target heals - White Mage
Healer with shields - Scholar
Healer in between - Astrologian

See.. that's how it goes in Final Fantasy XIV. Your jobs are your specs. That's just the way this game wraps it up.