We bought a Columbus (from Lofty Shelters) back when my first son was born. When my daughter was born, we could still fit, but it was pretty darn crowded. Now that we have three, there's no way we could fit.
Last year, we used a big ol' family tent. Yuck. Way too much trouble.
Now, however...
My older two (the oldest turned 8 today, the girl is almost 6) are now old enough to sleep in the Columbus on their own so the wife and I (and the 2yo) can have a tent to ourselves. In another year or two, all three will be "up top" and we'll be at the Marriott. Er, I mean in a tent. Or maybe a trailer.
The neat thing is, if it's not all of us, we can still use the Columbus -- this weekend my oldest and I are headed up to Mendocino National Forest by ourselves (dance class -- long story) so we'll just use the RTT.
I really like the height of the Columbus as well as the ease of opening/closing it (although tucking in the tent can be a pain -- works best if the doors are unzipped). The only problem I have is that the latch has rusted solid. Other than that, it's been great (and even survived me going in a garage that was way too short.)