Love my Extang Tri-Fold Hard Cover. It lets a few drops of water in from time-to-time (mostly from the tailgate area), but nothing to complain about in the bed of a truck. It doesn't fold open completely, but I can remove the entire thing in about 2 minutes.
I haven't pulled the trigger yet, but the G4 Elite looks great in that you can get in from the back or the front. They do a great comparison with the Bak G2 on you tube. I know a guy locally who is selling BAK products for $650, new in box, so may jump that way. Let us know what you decide.