I've stayed at both (plus the BWV) and enjoy each for its own reasons.
I loved the room size at Old Key West. The feeling of being away from it all was so relaxing. It was nice to have quiet after full days at the park. We didn't have a car, but honestly, I didn't miss it. When I'm on vacation, I like leaving the driving to other, and the buses were just fine. It was my first experience with
DVC and had a big hand in my deciding to join. When we opened the door and walked into our two-bedroom, my daughter-in-law just went, "A-h-h-h-h-h-h." That says it all.
I bought at the Beach Club, because that's what was available through Disney, at the time. I admit to being a little nervous prior to our first trip, because I'd read lots of bad about the BCV on this board. The air conditioning is awful. Water pressure stinks. Unfriendly CMs. Etc. But you know what? We didn't experience any of that? We had a wonderful time this past December, and I look forward to our second trip "home," this fall. I love the location. It's great to be able to walk to Epcot and the Boardwalk, and I love having the option of taking the Friendship boats to MGM. The bus situation could use some tweaking. The buses were almost always full by the time they arrived and we had to stand, but it did not take away from our vacation. I'd rather be standing on a bus at WDW than sitting behind a desk at work. Always.
Good luck! I hope your experience is as magical as ours no matter where you choose to stay.
Pat
48 days and counting . . . again!