When is your trip? I would personally stay somewhere that I've never stayed, so I would lean towards BCV or AKL. We have stayed at both (and WLV) and love them each for different reasons.
BCV - if you are going in a warmer month, the pool is nice to relax in. The kiddie area is pretty fun, and your daughter would enjoy that. There are movies on the beach that you could enjoy. You could walk around the lake during your evening. It would give you a feel for the entire resort area. Lots to take in, and a day off would be a great time to sample. Although, with Epcot just around the corner, I'd have a hard time staying away.
AKV - it is not our favorite resort. It is lovely; I like dark woods, and I adored waking up to animals outside my balcony each morning. I just personally prefer to have a walking option to a park. I tend to go to MK more when at BLT and to Epcot/DHS more when at BWV or BCV. I enjoy walking, and I like having that option. That doesn't make AKV bad, just not a good fit for my tastes. I bet your daughter would love seeing the animals. Kidani also has a wonderful splash area for warmer months. The savanna is a great way to spend time. I didn't use it, but I've heard there are great cultural presentations as well. It would feel very different from BLT in that it is secluded, so that could be nice.
I know I said "no" to WLV, but that is because you've already stayed at the hotel and it is the same resort area as BLT. It's still a lovely property that we enjoy a great deal.
If your purpose is research for the future, pick the resort you most likely would stay at, or the resort area that most intrigues you (in the action, farther away). Or, you could pick based on the theme that appeals the most. Or, you could draw a resort out of a hat! I guess I'm saying neither choice is bad. Enjoy your bonus day!!