I have a Rainbow that I use as a solo tent for wet conditions. It's huge inside (I'm 5'6"). It's fine in the rain if you seal the seams well. In my opinion two would have headroom but be cramped for width and space for gear.

For two I'd buy the double rainbow because of the double entrances/vestibules and the for the ability to rig the vestibules as porches to maximize ventilation.