It depends on what you're looking for. All three are beautiful resorts, and they all have their appeal.
I love OKW because it's quiet. It's been there a while, and the landscaping has grown up around it. It has a really laid-back, lazy feel to it. Also, you can park right in front of your building and walk right into your room.
Olivia's is a great restaurant, and the main pool is nice.
BCV is our home resort, so obviously I love it there, too. SAB is incredibly, absolutely the best pool on property, and the rooms are decorated beautifully. I also love areas like the Solarium and other kind of quiet, out-of-the-way places they have there.
AKV is also great. We've stayed at Kidani, but we haven't done a villa at Jambo. The savannas are obviously really cool, and looking out your window at a giraffe is almost surreal.
Honestly? I'd hit up the DVC boards. Read reviews. Look at pictures. It all depends on what you want out of your resort. As you said, the villas at OKW are bigger, which is awesome. BCV has walking access to Epcot and DHS, or you can take the boat to either location. OKW has a boat to DTD. Also, OKW has large patios/balconies with enough room to sit four people. That might be something to consider if it matters to you.
You can't go wrong with any of the three, tbh. If you stick with OKW I know you'll have a great trip!