I've had a pop-up and now a hardside. I didn't notice any difference in the way the truck handled. If a truck needs some suspension assistance I usually recommend SuperSprings because as an added bonus it really reduces sway too. If your truck doesn't need a suspension assist but you want some additional sway control a Roadmaster or Hellwig sway bar will take care of that (make sure your shocks are good).
There are pros and cons to pop-up vs hardside but unless you really need to duck under low branches or rock outcroppings, IMO, go with a hardside. My hardside is only a couple hundred pounds heavier than my prior pop-up.