Phantasy Star Online 2: New Genesis has changed more than just the gameplay and world of the franchise. While its classes may be the same ones that have been part of this online franchise since its inception, how they play and their skills have changed. New Genesis overhauled skill trees and how sub-classes work from PSO2. They no longer affect stats, but instead introduce ways to mix and match playstyles. Along with other new systems in place, which classes pair well together has changed significantly.
Sub-classes in New Genesis are much easier to unlock than they were in PSO2. Players only need to progress to a certain point in the story, which you'll likely be doing anyway to level up any character. Players will receive a tutorial quest to choose a sub-class, and that's it. Like before, sub-classes can be changed at anytime, just like main classes.
A major new addition is multi-weapons. These are two different weapons with the same name that can be fused together, allowing classes to use weapons they normally wouldn't have access to -- which is great for some sub-class skills and makes them more effective to use. Here are the best sub-classes in the game and how to use them.
Hunter
The class with the most defense and HP, Hunter is once again great for survivability. However, they don't have the same great skills they once did as a sub-class. As a sub-class, Hunter skills generally pertain to defense. If you're planning on mostly playing the game solo or are just having trouble getting dodges and blocks down, this sub-class may help.
There are better options in terms of sub-class skills, but if you're planning on using a multi-weapon, then Hunter is a great choice for Fighter as it benefits from access to additional melee weapons and heavy hitting attacks. It also pairs interestingly with Techter, as you can essentially play a Hunter who heals and buffs themselves with a Talis/Hunter weapon combo while also having a few spells on the side.
Fighter
As a sub-class, Fighter can provide extra damage in big boss fights, similar to Hunter, it's a bit more self-contained. It also has a PP regeneration skill, but it's situational and there are other sub-classes better suited for that. Fighter has access to some fast and powerful melee weapons and Photon Artes, meaning melee classes will benefit most from this sub-class.
Fighter is the perfect choice for Hunter if you're looking to make a heavy hitting melee class with some crowd control functions. Like, Hunter, it's also good with Techter as a main class, but it can also pair well with Gunner like in PSO2. Gunner is a medium to short-ranged class, and having a boost to attack and access to melee multi-weapons to clear close enemies is helpful.
Gunner
As a sub-class, Gunner is mainly good for regenerating PP quickly -- something that's useful for any class. Best of all, there are basically no situational requirements for these skills, making it easy to use. For multi-weapons, Gunners tend to stick with Twin Machine Guns, a short to mid-range weapon that's not very powerful outside of its main class use. However, it does get some good evasive skills if you're in a pinch.
Gunner works with any main class thanks to its PP recovery skills, but can really shine when paired with Force, Techter or Fighter. These classes tend to go through PP quickly. As a sub-class for Fighter, it also offers some additional dodge moves and a new way to attack at close range via multi-weapon.
Force
Force is easily one of the best sub-classes currently in the game. It has a natural PP regeneration skill, as well as one that triggers when enemies are defeated, making it even better than the Gunner's skills. On top of this, Force is one of the only classes capable of doing elemental damage and status conditions -- and having a multi-weapon with a Force sub-class gives anyone access to most of these Techniques.
This makes it invaluable in any Urgent Quest, PSE Burst and Gigantix fight, as there is a higher chance to down these enemies, then do serious damage with main class weapons and skills. Force as a sub-class pairs well with every main class and will likely continue to after Braver releases.