I would buy one MK resort, one Epcot resort and one "out there resort". This way I could do split stays and always stay near the park I intend to visit.
For the MK I'd probably say BLT for the convenience, but I'll stay there for the first time this September and I'm not entierly convinced about the theming. If I end up not liking it, the second best for me would be VGF.
As an Epcot resort, I'd go with BWV, for better views, the chance of the standard rooms and easier walk to DHS. While I like Stormalong bay, I prefer the theming and slide at the Luna Pool.
The "out there" category includes AKV, SSR and OKW. AKV is one of my favorite resorts overall, so I'd buy there, but SSR with DS in walking distance is nearly as attractive.
The reality is that I own SSR and I've been able to use my points to sleep around with quite some success. So until now I haven't felt the need to own multiple resorts.