That’s a really hard question as they are both wonderful resorts and our two favorite deluxe resorts (YC, too).
Nothing beats the proximity to two parks when staying in the Epcot resort area and SAB is awesome. That said, my one hiccup with YC/BC is the lack of quick service options. We are always stumped as to where we should eat quickly when we stay there. The Marketplace does not have a lot of options unfortunately. Yes, you can always walk to the Boardwalk or even head into Epcot, but sometimes that just isn’t feasible with our plans.
We adore the Poly. There is something magical about walking into the lobby and seeing the castle across the lagoon. I love hearing the train whistle when walking around the resort. For two adults, I think the resort is romantic with the tiki torches and Hawaiian music piped in. I love the pool (it is on the small side), but the quiet pool is just as nice. I also like the food options at the Poly - there is a nice quick service option, plus Trader Sam’s is there, too. You can also hop on the monorail and be at two other resorts with great food options in a matter of minutes. Many mentioned the lobby full and chaotic, but we never feel it’s that way. I think the lobby at the BC can also be full and chaotic because of Cape May Cafe and lots of families are there, too. I think you need to figure out which park you are going to spend the most of your time and make your decision off that. I know if you switch to the Poly, you won’t be disappointed.