I had an Avalanche for about ~4 years, and quite honestly, HATED the cover system on it!! The panels were heavier and bulkier than necessary, IMO, and they took up too much bed space if you got somewhere and wanted to load something in the back. Otherwise, pull them off and leave them at home, but again, I found it to be just a pain in the ass the whole time I owned that truck.
I opted for the Bak-flip VP for my '14. Quite happy with it so far. My only real "complaint" is that release cables can be finicky to grab a hold of sometimes, esp. wearing gloves (which I often am right now in the winter!), so I wish they were a little easier to grab. Otherwise, works well, easy to use, and no worries about having to take the cover off completely any time I want full access to the bed.
I still think the Roll-X probably would be just about the best solution, but I worried a little bit about how well it would perform in the cold/snowy winter environment, so went for the Bak-flip instead, but there will always be a part of me that would rather the Roll-X (quicker/easier operation, and still have visibility out the back when it's rolled up).