Just ordered a Fold a Cover G4 Elite from the factory store. I'm getting it because it has the least minuses against it. I like the security and the hard cover. and I don't have to worry about drainage lines and such being a top mount.
I don't like the fact it won't fold up all the way but being a 4 panel, the front is still easily reachable and it is removable in the event I need the whole bed. I'll have to carry a 7/16 wrench though if I need to remove it though.
I used a coupon code TDSFAC2015 on the factory store to get another $25 off. Free shipping, 2 year warranty and a tailgate seal sweetened the deal. I'll post up some of my thoughts when I get it.