We got front air on our 17 ft. Casita
. I would do it again. I like having the vent (with Fantastic Fan) over the bed. (Roof air is mounted in that vent, with another vent cut forward, in the galley area.)
Drawbacks of front air are:
1) it eats valuable closet space, and
2) some say it doesn't circulated well to the back of the trailer. (I've not had this experience, but, honestly, in the summer we high-tail it to the mountains, where we don't need a/c, except for the trip up and back. Otherwise, we're not big on camping in hot weather.)
I'll let someone with roof air extoll its virtues for you.