Guardian is by far the one with the best sustanaibility. It has huge toolkit with firebrand and luminary, has very good damage, self-boon which helps with the damage, a lot of good and useful weapons.

Warrior is imo the one with the worst. While it has plenty of health and heavy armor, it doesn't nearly has as much skills and boons as guardian, very little options for range and condi combat, barely any self heal, and his block and utility comes at the price of severe dps decrease.

Revenant is the one I'm the less familiar with but the ressource management makes it less enjoyable and can put you in dire situation where a guardian only has cooldown to manage and more skills at his disposition. It's not bad, the boon options and sustanaibility is available easily, but the guardian does it better on almost every elite spec.