Well let's start with downsides of a pop up camper first.
A quality pop up is usually more expensive than a hard sided camper.
Generally a pop up will have smaller tanks, maybe no fixed toilet, possibly no shower inside.
Most pop ups are not well insulated. Aluminum frames transmit heat/cold. Often the floors are just wood, no insulation.
Moisture is an issue in any small camper. As already stated, air flow is the fix. The first place is see condensation in my four wheel camper is on the ceiling. On the liner than contacts the aluminum frame, and on the aluminum hinges for the lift panels.
Not all soft sides are created equal. Palomino as an example is a joke. Four wheel campers soft sides are pretty solid. With the insulated liner, it is relatively quiet, dark enough to sleep, and reasonably warm.
Some pop ups do not have the room to leave a bed made on the cab over. Often times requiring a slide out anyway, so you will be making a bed every night and morning versus just crawling into bed. The bedding (and cushions) also takes up storage space.
Depending on the lay out, sometimes with the bed made, you can't sit at the dinette, or you can't use the sink, stove, whatever the case.
Some configurations make a large part of the camper inaccessible with the top closed. So a quick roadside stop to make a sandwich or coffee or whatever may be more involved.
On to some of the pros of a pop up.
Since they often have smaller tanks and less storage, weight is usually kept down compared to a hard side.
Center of gravity is lower.
It is easy to have roof racks, and be able to carry kayaks or paddle boards, or a roof top storage box.
Wind drag is reduced. Although in my experience not as much as you would expect. I think there is a bigger difference encountering cross winds, but overall wind drag isn't hugely different assuming similar width.
One of the biggest differences to me is the overall size and feeling of the rig when driving. I usually leave my camper on, jacks removed. Added height is minimal, width is barely effected. Handling is good enough that I don't mind leave the camper on all the time, and it fits in my garage with room to spare. My last hard side camper was miserable to get off the main road. Way too tall, I was pushing tree branches every where, and there were a lot of places I simply had to back up and couldn't fit. This basically defeated the purpose of the whole setup for me. Additionally because of the size and handing, I only loaded the hard sided camper when I was going to use it. It didn't fit in the garage. So I had to pay for storage, it was a pain to pick it up, I left the jacks on when using it, which made it even wider.
All in all it really depends on how you want to use the rig. Like I said I leave my four wheel camper on most of the time. In and out of the garage, out of site. No issues with coffee drive thrus. The additional size doesn't come into play much off road. Only with very low hanging branches and off camber spots with trees. My camper is usually packed with food and snacks, bedding, everything we would need to support the family for several days if needed. It is really convenient for day trips with my daughter, or last minute over nighters. With the hard sided camper, every trip really had to be planned out, pick up the camper, load everything in, pack food in, etc. It was the difference between "hey lets go to the beach for the night" and "do you really want to spend a bunch of time loading and packing the camper, just for one night, then unpacking and unloading again the next day?"
Everything is a compromise.
