This is an important issue. Of course, the tradeoff in going with a hard side vs. a pop up is overall height. To a degree. Here is a pic with both the smallest hard side and one of the largest hard sides, mano a mano.
As long as clearance is not an issue (length/height/width/underneath/approach/breakover/departure) you don't need 4WD, I'd take the one on the right any day on a long trip.
My bro has a palatial 9', 92"W OUTFITTER! on his stock height 4WD '99 F-250/International/6 speed manual long bed pick up. My short bed Dodge has a 3" lift, larger tires, adorned with a stock height '98 Lance Lite(no AC on roof. Only the usual vents and 200Watts of solar panels) The difference is about 16" in total height. Here is a comparo in Death Valley:
You can see the big dent behind the driver's door bro got because of lack of clearance which was obtained rounding the bend at Mengel Pass right here:
There is no overhead clearance problem anywhere in Death Valley but to be narrow is a good thing.
It's simply all a trade-off. I agree with a former poster who said width is more important than height. But that all depends on where you go. In dense forests simply small on all fronts is imperative. On a "Volcano Tour" around the Pac N.W. a few years ago, the forest was so dense that there was little opportunity except on wide dirt roads to get remote. The trees were just too close together. A dirt bike would have been the best mode of transit, or on foot. If you want to fit your camp mobile into a shipping container to get around the Darien Gap, you are out of luck with a 4WD TC.
Our TC is 20' long, 10 feet, 4 inches tall, and with the short 139" W.B. and front coil springs will allow you to turn a very short circle. We have driven it on the "Road to the Sun" in Glacier N.P. It was white knuckle as we had to drive into the opposite lane occasionally to miss overhanging rock formations; my wife Jeanie hanging out the pass side window giving me clearance indications as we crept along under the overhang.
My bro's F250 has front leaf springs and a longer W.B.(160"?) He had to 'double pump' many of the sharp curves on our Death Valley trip. So, turning radius is also something to think about.
The other obvious thing is to leave the jacks at home. Just pretend you are a class C and nothing can be detached.
It's my observation that there are a lot of 1-1/2 to 2 ton box vans moving cargo hither and yon in Sud Amerika. That should clear the way for a narrow TC.
Most of the reports from people who have ACTUALLY driven in Central and South America said 4WD was unnecessary. However, when we get near a beach in Baja with our rig, we are mysteriously drawn to drive on the sand; For as long as we can; Because we can.
So, the bottom line is: There is no perfect height. Or width. Or length. Just make it as small as you can and follow someone bigger than you.
jefe