YC and WL are our favorite resorts, so I understand your dilemma. I prefer YC over BC because I will always get a full balcony. That being said, here are the differences:
1. Theming theming theming. WL is amazingly themed, better than BC IMO. Plus due to the design of the resort you are in or walking through the lobby a lot, which is amazing. I could just hang out in WL's lobby or in one of the nooks overlooking the lobby. Not so with BC. However, if you are from the Pacific Northwest you may not be thrilled with the theming since it will look just like home. Not so with this Florida girl - I am sick to death of palm trees!
2. WL is a much more compact resort which means less walking.
3. WL has a real (though some would maintain too small) quick serve while BC just has the Marketplace with a very limited menu.
4. WL offers easy access to the Contemporary, Fort Wilderness, and the monorail loop. It also has the best straight-out-of-MK boat transportation of any of the lake resorts. You just go straight ahead out of the exit and climb onboard, so nice and close.
5. BC of course has that awesome walk into Epcot, but the price is paid with busses that could share with as many as 4 other resorts (YC, BW, Swam, Dolphin. I personally find the walk to HS to be rather long from there, but the boat is pretty easy.
6. You have a good probability of not having a full, or any, balcony at BC.
7. You may end up with a walled balcony with a hole in it at WL. I don't like them. But the possibility you get that versus the possibility you get a standing-only balcony at BC is smaller. You could also smile and ask nicely at check in at both places to ensure your balcony needs are properly met.
8. Stormalong Bay. I love love love that pool. If you want to build a sandcastle, feel the sand on your toes, float in a lazy river, swirl around in a whirlpool, enjoy the splash of a waterfall, or go down the longest slide on property, Stormalong Bay is the place. We have contemplated ignoring our Le Cellier reservations just because we didn't want to get out of the lazy river. It's that great.
9. On the other hand, WL's pool, though much smaller, is beautifully themed, with a stream running down rocks into the pool, two nice hot tubs, and a geiser that goes off every hour. It's much quieter and less crowded.
My family has decided that if lots of pool time is our goal, then we will go to YC, and we have done several one-night-only-no-parks stays there, just to enjoy the pool for a day and a half. But if we are coming during non-swimmiing months, WL is my happy place. I love love love that resort.
I hope this helps!