I never went the pop up route for a few reasons; One I did not want to be putting up and down. Had a tent trailer and that was a pain so did not want to do that with a TCer. Second was the Northern Lite that I bought came in at 1600 lbs and a pop up that I was looking at was over that so did not have any possible weight savings and finally was the winter camping - in a hard sided it is warmer, but I am talking -20 to -30 type camping.
For me I do not have to worry about low trees, around here a low tree is a tumbleweed and we drive over them. Plus I really liked that I could load a hard sided cupboards and not have to put things in different places when traveling.
The downside with a hard sided is you have more camper hitting the wind when driving, not a lot but about double from a pop up, and that effects the MPG more than the weight does. How much I never really figured it out but all the other benefits outweigh the MPG savings that I would get in the pop up.