We love our 2005 Fleetwood Allegance shown in the profile pic below. We purchased it used in August 2008 and have put around 15,000 miles on it since, including a two week, 5,000 mile road trip from Colorado to Oregon, Washington, California, Nevada, and Utah. We've camped next to the Pacific Ocean, at Mt. St. Helens, Crater Lake, and all the way to 10,000 foot elevations in the Rocky Mountains.
With it, we've been able to take some trips that we otherwise wouldn't have. We spent a week in Mesa Verde NP, Colorado; two separate week long stays in Custer SP, South Dakota; plus that nice long trip previously mentioned.
Previous posters mentioned setting up to load & unload. This depends upon the exact floor layout. With mine, I can open up the door while the top is down and access the pantry cabinets, fridge, 20% of the other storage cabinets, plus about 65% of the floor space. That makes loading and unloading pretty easy.
We get the same or better gas mileage when towing (slower speeds & gentler on the gas/brake). I've modified the suspension to raise the height by about 5" so I can take it on back country roads.
We intentionally chose a model WITHOUT a toilet or shower. They take up a lot of floor space and I didn't like the idea of somebody doing their business just feet away from where I'm preparing dinner! If we are boondocking we take a separate toilet & privacy tent. When in a developed CG, we use the facilities we are paying for.
We have hot water, fridge, furnace, and outside shower (no air conditioning). The 2kW generator provides adequate power for everything in the pop-up, and then some.
We've camped in bear country and don't worry about it. Keep the trailer clean and handle food/trash/toiletries as if using a regular tent. We've used the camp provided bear lockers, hung bear bags, or put them inside the vehicle at night.
Two huge advantages the pop-up has over a TT are: 1) I can easily load a canoe or bike rack on top of the pop-up and b) I can store the pop-up in my garage for FREE (HOA restricts outside storage).
Now that you've read my praise, it's time for the cons:
Small 13" tires: to get the necessary load ratings I'm stuck with 8-ply bias (load range D). This limits where I can get a wheel/tire assembly in an emergency. I've not had a blow-out on the road, probably because I keep them inflated to the max pressure, know my loaded weight, store the unit in the garage, and keep my speed in check. If it's really hot out, I reduce my speed too.
In the almost 6 years of my ownership, I've closed it up wet only a few times. It's pretty easy to set up and allow to dry when I get home. In Colorado, the tent material dries pretty quick.
My pop-up has an aluminum roof, so it gets incredibly LOUD during hail storms. The pop-up has come through some pretty severe weather without issue, including 80+ MPH wind gusts. DW & I didn't come through as well though!
And lastly, the door has a lot of air leakage around it. Our solution is to hang a blanket in front of the door. We use a cheap fleece blanket with small spring clamps on an aluminum rail at the ceiling. This also helps cut down on how often the furnace runs. The blanket is pulled aside during the day.