Phantasy Star Online 2 is mostly a skill-based game, with a continually fluctuating class balance. Nevertheless, in any game, a certain balance will be found in which certain classes stand out compared to others, for a variety of reasons.
For that reason, I’ve decided to rank the classes of this game primarily based on versatility rather than raw power, as being an MMO (and an action MMO at that), every character can pretty much do any content if the mechanics gel with you well enough.
Gunner is the premier ranged class of the game. While Ranger is quite good (and leveling it or Braver to 30 is a prerequisite for unlocking Gunner), Gunner has a lot of sheer single target killing power that the Ranger relatively lacks.
Gunner is good as the main class and sub-class, which is what marks it as being a great fit for this list.
The Fighter is to melee combat what the Gunner is to ranged combat; simply a great all-around melee combatant with access to a good variety of weapons and dual-wielding capability.
Much like the Gunner, Fighter is the good peanut butter to other class’ chocolate. It mixes well with a wide variety of other options both as a main and sub-class, including with Gunner itself, for a versatile switch hitter playstyle.
Hunter is somewhat the odd duck for this list, being a class that usually isn’t suited as a main class. Hunter is basically the primary “tank” class and uses a wide variety of large weaponry to duke it out in close quarters.
That role in itself (besides the large weapons) isn’t super unique, and likely why it isn’t much chosen as a primary class. However, Hunter mixes well with almost every other class in the game, augmenting the strengths and shoring up the weaknesses of a variety of other classes. Pretty much everybody likes a bit of extra durability.
Hero is a “Successor class,” a sort of uber-class that is balanced by not being able to choose a sub-class (though the other two Successor classes can at least be chosen as sub-classes; this is not the case for Hero).
Heroes do high damage and are relatively easy to use, but are limited by that relative lack of versatility and the fact that they must be unlocked first by getting to a very high level with another class. In essence, unlike the other three, the Hero class is probably a stronger choice for “best” class in terms of raw numbers, but in terms of versatility and new player friendliness, they are quite a bit worse.