BW/S/D are always on the same route. Usually, BW is picked up first, and dropped off first. But, I have been on a BW bus that went directly to a park, with no stops at S or D.
YC/BC always share a route. YC is first, obviously.
But....there are times that all three are on the same route!! Usually, park opening and closings bring the two different groupings....BW/S/D and then YC/BC. But at less busy times, all of them could be lumped together.
Many people say this is an awful system, and that other resorts don't have this system. BUT....if you stay at POR you are going to make 4 stops, within the resort. Same at the other moderates! Other deluxe resorts will include other stops at other resorts.
I have stayed at both BC and BW. I own DVC at BWV. I love it there. I don't think I would ever say that any room is shabby, at either of those two resorts. BWV just had a complete rehab about 2 years ago. BC may be getting one soon. But, I wouldn't worry about staying there at all.
If you just care about the buses, then go with BC. The buses go to only MK, AK and DTD. The buses to DTD are miserable at all resorts.