We've stayed at the Contemporary garden wings and have often stayed in a one-bedroom villa at the Boardwalk, but not at Key West. We loved the convenience of the Contemporary. However, with the group you have, which includes both your husband and your mom, I would pick the one-bedroom villa at OKW hands down. Like ErinInCT, I think you'll be much more comfortable if mom and DH aren't trying to share the same sleeping space.
The buses aren't that inconvenient, nor is the drive to the parks if you have a rental car.
The space of a one-bedroom villa, including jacuzzi tub, bedroom separate from the living room, full kitchen and washer/dryer will, IMO, more than make up for the less convenient transportation. I understand the villas at OKW are considerably larger than at BWV so you're bound to be very comfortable. OKW is also very pretty and scenic and Olivia's Restaurant is delicious.