I had a TonnoPro tri-fold soft cover on my Tundra and it was great. It would take a driving rainstorm to get a little bit of water showing up on the walls of the bed, but kept everything inside dry.
Now I have an Extang Solid Fold 2.0 on my Ram, it's great too. Same thing, keeps most water out, but every once in a while I'll see a little leak down the wall... never enough to get anything wet though. Benefit of the solid fold is that it is more secure and I can mount things (currently bikes) on top of the tonneau when I am hooked to my trailer.