I'm going to be getting G a new bed/frame. I can't decide if I want a twin/twin bunk or a twin loft bed (open space underneath).

Without getting too much into specifics does anyone have recommendations one way or another?
We are not having anymore children so it's just him.
The room can accommodate either.
He doesn't care which one we get.
We have one mattress/boxspring already so a bunkbed would require us to get another mattress. But we have no guest room so it'd also give us another bed for guests.