Davey, I've got both, (and a Scout 11 for that matter.)
I like them all.
I think the winner is the ShopSack. It's simpler. When I'm on a tour, I just throw stuff in. With lots of little pockets, I can't remember where I put what. With only one choice, I know it's all there. Also, the ShopSack opens nice and wide on the top, and it holds more. Also, the ShopSack is more useful when not in the basket.
Re the Scout 11, I know it's not a basket bag (the Scout 14 is.) With that said, the Scout 11 is very useful as a handlebar bag, or as a racktop bag, particularly if you need a bag to easily switch among various bikes. I think I rate it ahead of the TrunkSack.
So that's my 2 cents. But they're all nice bags, no question.