If Squeenix doesn't get rid of the silly 'you must do it solo' restriction for the instanced Story Missions, all my characters will end up being Marauders and Gladiators. Because I heard those are the two classes with the least trouble when soloing. Not all of them will be so ICly, but besides roleplaying I like to actually play and enjoy the game. And those solo missions? I don't enjoy them at all.
With that said, I normally make my characters picking the class I want to play. In the case of ARR, though, I'll probably have a bunch of OOC classes in my main so I can cover all roles for party play.
If one of my characters ends up having various classes ICly, then changing them will be handwaved like the game does: it's my character using another weapon or, in the case of some magical classes, using different spells.
With that said, I normally make my characters picking the class I want to play. In the case of ARR, though, I'll probably have a bunch of OOC classes in my main so I can cover all roles for party play.
If one of my characters ends up having various classes ICly, then changing them will be handwaved like the game does: it's my character using another weapon or, in the case of some magical classes, using different spells.