The Columbus was my first Autohome RTT and my wife's favorite because she could stand up to pull up her jeans. I have the Extreme in the small and my wife and I have plenty of room inside. I like the rack on the top for additional gear so that is my favorite.
In a earlier post you asked, "So what is the difference between the AirTop and the Maggiolina? " Think about the way the tents open, the Maggiolina line all the tops go straight up "Vertical sides". The Air top is one of the Maggiolina line and it uses Gas struts to lift up the top. The Columbus has "Vertical sides" the back is sloping and the front is a sloping hard top.
Apologies for coming in late, I have a small Columbus Variant on my LR3.
How tall are your adults?
I ask b/c when we were buying our tent last year the folks at Autohome noted that taller folks tend to want the XL just given the nature of the clamshell. For us, being 5'5", there is more than enough room for both of us (I would say it likely would be good enough for anyone under 5'10" or so, maybe even 6')...assuming commensurate width.
So for two hobbits, as my abnormally large friends like to call us, the S is fantastic.
So the wife would def be happy...you may find it a little small...from what I've heard the complaint most often is that your feet will brush the bottom of the clamshell. The Autohome folks may be able to chime in and offer their experience.
I'm 6'1" and 200 lbs. I have no trouble sleeping in my Maggiolina Extreme (small). My wife is tiny and we both sleep well in it. My son and I sleep comfortably in it on hunting trips and he is almost as tall as me.
My feet do occasionally touch the bars at the end of the tent but it in no way effects a good nights sleep for me.