Our 17 has the AC in the wall. We could've gotten it on top, but wanted the vent-with-fantastic-fan over the bed instead. (Ours is a '99; at that time they weren't even offering the additional vent over the galley AND -get this- our salesman actually advised against the rooftop AC because "it spoils the look of the trailer.")
In other words, AC in the wall or on top is up to the original owner. I think now more folks opt for the roof mount, but if height were a concern (or "the look of the trailer"
), the wall mount was (is?) still available.
By the way, I have NO regrets about our AC-in-the-wall!