I have a door that goes to the outside from my basement. Right now its a
hollow core door (I know I know, it was there when I bought the place), and
that hollow core door has swollen shut. For the most part I'm inclined to
just let it do nothing, swollen shut it certainly doesn't leak air. But
sooner or later I will want to replace it, door frame and everything.

So when that time comes, assuming the door will be in damp conditions, what
would be better a steel door or a wooden door? I'd be inclined to say
steel, thinking that wood would swell and warp and rot in damp conditions,
but I wonder if steel would just rust. I don't care about looks per se,
just durability and air/water tightness.