Everyone has their preferences, and certainly the karve is better for navigating rivers if that's what you want to do, but it's useless for hauling anything, which is my primary use for a ship. If I want to explore a coastline or river, I just get out and run.

I don't think the draft of the karve is much, if any shorter than the longship, although the longship is wider, of course. The benefit of the longship in near-shore, possibly rocky situations is that you don't have to care. The longship will take a huge amount of damage. The only issue is possibly getting stuck, but that can happen in either ship, and I think the longship has more power to pull you through.