It all depends on what parks you tend to spend the most time in. Here's a breakdown, sort of..
BLT....smallish pool area, quick walk to MK, monorail to Epcot (have to transfer at TTC).
VWL....nice pool area, decent food court if needed, kids seem to love the theming, lobby is incredible (both WL and DVC area), boat to MK, buses everywhere else.
BWV....love, love this resort. Nice pool areas. Boat to both Epcot and DHS. Nice walk around the lake. Walk to Epcot...under 10 mins. Walk to DHS...under 20 mins.
BCV...great pool for kids, nice cheery theming. Quick walk to Epcot...about 6 mins. 20+ walk to DHS. Boats to both.
OKW..larger than normal villas. But I find it to be confusing in there and the car traffic makes it sometimes a bit dangerous.
SSR..have yet to stay here. Far removed from the parks.
Kidani...love this resort as well. The addtl bathroom in the one bedroom villa is a huge plus. And the pool area is terrific.
The buses at all the DVC resorts tend to be less than wonderful. Yes, the BWV buses will also stop at the S/D, and there will be times they will also be combined with the YC/BC guests.
If it were me, and I was looking for a villa for your group, I would recommend either BWV or BCV. It will still be hot in Sept, so the pools will be a huge draw. I like the ability to get to two parks easily. A two bedroom villa will be perfect.....a master bedroom in the one bedroom, with the sleep sofa in the living room. Then the queen bed and the sleep sofa in the attached studio. I would imagine that one set of adults could take the master, the other two the studio with the kids. If one of the kids in under 3, you can use the pack and play as the bed, in that studio. That would keep the living room free from sleepers.
But in all reality?? There are pros and cons to each of the DVC resorts. What some lack for in transportation, they make up for in park proximity. Or some theming may appeal to you while others don't.