I would like to remind people that they have said they are most likely only sticking to PHB, so let's not suggest anyone beyond that.
I suspect they will release these as they become done. Not that the current classes feel "done" either, but it seems they released the "origin classes" first, and ranger. (Ranger actually feel the most thought out and functioning classes)
Personally I want to play a Paladin. So that get's my vote
They have only said they're aiming for PHB, which is why I hesitated to mention ones from other books. I decided against limiting myself to PHB though, as I don't think it means we shouldn't mention ones we would like to see from other books, as the more people speak about non-PHB subclasses the more visibility they get, and the more we can at least hope we may get at least some of them.
You're likely right about them releasing classes as they're "done" as well. It's really the only thing that would make sense.
Paladin is a great pick too. I was torn between Bard or Paladin personally.