A hunter/ranger would make sense, since neither of the first two are anything like that. We also don't have a Sword and Shield companion nor a rogue.
Course there is no rule that says the new companions have to be completely different classes than the first two.
I hope one is a rogue as that may be the only way I play one as they just don't seem very viable to me so I wouldn't want to waste my PC's on one.
