I would lean strongly towards Banewarrens unless you have some reason to do otherwise. I picked up CotSQ only because my current campaign is already in a situation very similar to that in CotSQ, and I hoped to plunder significant parts of the adventure. Some of the stat blocks, creatures, and characters look useful, but I feel like I paid a lot for what I got. CotSQ did not strike me as especially creative; it just seems like a long dungeon romp though the underdark with lots of fighting.
The banewarrens, on the other hand, has a variety of characters with unique motivations, a variety of locations and situations, twists and turns, overall a more creative adventure AFAIAC.