I personally have white metal for the aesthetic look but wooden is nice if it's also white. Metal is easier to clean in case anything gets spilt, drawn on, sticker residue. But it's also nosier if the plastic eye of a teddy bear bangs on it in the night and I've had trouble with squeaking before after years of use and LOs jumping on it.
We have ikea wooden beds and would get again. Easy to paint whatever colour the kids like at that particularly point, and easy to cut the legs down etc. if they're little and the bed is a bit too tall...
Saying that though I'm sure a metal bed would be fine - just personal preference really.
We have bunk beds and I vetoed metal ones because they squeak. So we've got basically high gloss finish bunks with proper stairs and bookshelves built into them. Look great, really sturdy... fucking pain in the arse if you ever need to move the buggers.