I think BA might be considered a little better than BD, but from looking at the Deck Plan on the Princess.com website, it looks to me like the only difference is that it's in the Caribe deck instead of the Baja. Take a look at the Princess.com Website, click on Deck plans, and you can compare the two locations! They look pretty much the same to me!
The letters just refer to the different classes of cabins. You can check them out on Princess.com also. GG, for instance, is an obstructed view so that would be one to avoid!