I'd say class.
Simply because, if we are given these five choices, it's safe to assume that the game in question would feature all five.

And generally speaking, 'class' is the starting point, because it dictates the limitations on available weapons, as well as class-specific abilities(which include the handling of a pet).

Also, like classes are forged from like nations.
That being said, if nations are limited to certain classes, my nation choice would be based on the available class options.