We've stayed at both. BWI multiple times and YC only once . . . so you can probably guess my answer!! I found YC to be very subdued and very much a convention resort (you may see people in business meeting attire in the lobby). There's just really nothing going on there! If you like that atmosphere, it may be the right resort for you.
We LOVE BWI! We love the theming, the variety of TS and QS on the Boardwalk, the entertainment on the Boardwalk in the evening and the ability to walk to both DHS and EP (BWI is closer to DHS). My DS9 also actually prefers the pool at BWI. The slide is faster and I like the fact that everything, including the pool bar is accessible and visible from the pool deck (at YC/BC's SAB, it's very spread out with the pool bar outside the gates and the entrance to the pool slide across the walking path). At BWI, I love that I can see my DS9 wherever he is in the pool and I can even see him when he's waiting to go down the slide.
Even if YC were cheaper, I would still pick BWI over YC any day of the year!