BWV, BCV, and RIV are all sort of fighting for the #1 spot for me so here's what I'd say for all 3.
BWV: The fact it's a 2042 resort. I also don't love any of the lunch/dinner options at Boardwalk Deli. Usually just settle for the reuben.
BCV: Again, the fact it's 2042. Again, I don't love any of the lunch/dinner quick service options at Marketplace.
RIV: I don't like that I can't walk to a park. I don't like the restrictions. Also, I haven't found anything I love on the Primo Piatto menu.
As a bonus I'll talk about my other 2 home resorts:
PVB: Always feels crowded. Not the most streamlined luggage process (at least in my experience, taking Island Tower into consideration here). Not the most walkable to MK.
VGF: Travel time/proximity to the other 3 parks.