There are 16 different classes with over half of them being third tier and final tier classes. As such, there is such a huge list of classes to give to each MLP character (including Alternate styles of classes). So, what classes would each character have?

This is my opinion on what each of the Mane 6 would have for their classes:

Applejack - Duelist
Pinkie Pie - Bastion Warrior
Rainbow Dash - Full Metal Jaguar
Rarity - Astral Crusader
Fluttershy - Mastermind
Twilight Sparkle - Galactic Knight

What do you think?

The fact that there are six fourth-tier classes makes imagining the mane 6 on Mira a little easier.

You're right, Fluttershy would definitely be a Mastermind. No doubt there.
I can see Twilight swinging a photon saber with telekinesis, and forgoing the psycho launchers for pure magic blasts, just like in S2E26. Now that I think about it, she could easily be a Bastion Warrior, too, with her shield and gatling horn combo.
Rarity seems good for sniper support, so yes, Astral Crusader.
Hmm... the other three are harder to place. I can't decide.

Of course, who said they have to be stuck in one specific class?

Now, say the mane 6 were BLADE members. What divisions would they be in?

Rainbow - Pathfinders or Harriers
Rarity - Prospectors
Applejack - Interceptors
Fluttershy - Mediators
Pinkie - Curators
Twilight - Reclaimers

I'd say Rainbow's division depends on the author, and whether they like a canon Rainbow or a personal head-canon Rainbow. The first kicked a dragon, and is fit for Harrier duties, the second varies.