A truck cap gives you more room to haul things but I ended up wanting to haul things that were too tall and so on. The visibility is cut way down with a truck cap as well. It does lock though so things are fairly secure although somewhat visible. Lots of dirt on back door so visibility gets poor again. Tundra rear power window not much good with these units obviously.
The snap down cover is the least cost usually but drilling all those holes in a truck wasn't for me and doing them up can be tough plus things aren't real secure if somebody wants to steal things.
The hard cover one piece that tilt up at the back looks clean and color coded but pretty much limits you to hauling what you can get under it or how many have seen these tilted up with somebody trying to haul something. Can be locked though. Perhaps maintenance on the gas shocks.
Those 3 fold covers are more useful than the tilt hardcover. I assume you can get these to lock. Don't consume bed area like a rolltop whose storage can is under the cover at the front usually.
I have been using a Pace Edwards rolltop cover that has aluminum slats in it for some support for snow etc or if you ever want to put things on it plus a knife won't cut through it for security sakes. It locks but covers the bed stakes. It takes up some box room as the can that it rolls into is under the front of it. Some manufacturers models have this part above but then you can see it sticking up behind your back window. They do not go over your tailgate so a separate lock, have used a POP A LOCK, put into your tailgate if it doesn't have one is the option. I find mine collects dirt and some water at the rear but this is mostly due to the seal around the tailgate. If I'm on dusty roads or raining out I put anything I want dry into a big rubbermaid container that will fit under the cover. The Pace Edwards can that the top rolls into has a drain hole and hose on each side that you run down through box to allow water to drain out. Generally these roll in and out without too much fuss but I'm not sure if they are all great with snow on them etc.
Lot's of guys buy a wooden sliding drawer assembly and slide this in thus you can put things in the drawer and roll back the cover if you need to haul larger things like a deep freeze still or a couch.
Several options and several pros and cons
thats my 4 cents

Oh had one more thought..1 thing that mine offers is that I can open my tailgate to take things in and out without having to open the cover. That may be a pro or a con again as you get a better seal if it wraps over it but tougher access.