I would recommend offsite. We rent a house every visit now--we actually sold our DVC, because the kids liked the rental house better. A house offers a ton of room, not only can you spread out, but it's so easy to accomodate different interests, nap and bed times, etc.
I've heard wonderful things about Bonnet Creek--I'd love to try it, but the gang likes the house. BTW, we rent through Romancing the Mouse--we call it "our house", the kids don't want to stay anywhere else.
If on-site is what you really want, renting DVC points is probably the way to go. It would be worth pricing out the AsMu suites and FW cabins, too.
You don't list your kids' ages, but I'll tell you what my gang likes best about the rental house:
DD15 loves having her own room with her own bathroom--a luxury she doesn't get at home. She also gets her own TV in there, and free wi-fi. if she had mini-fridge in her room, we'd never see her. Plus, she runs, so the gated community gives her a nice, safe place to do that. I'm sure there are great places on Disney property, too, but she can do it at Windsor Hills, easily.
DS13 likes his own room and the free movie/video game rentals.
DD7 and DS4 like sharing a room (since they don't get to at home, at least not with each other). It's easy to put them to bed, then have others stay up and watch a movie or something.
Everybody likes the private pool as the best thing, hands down. They also like the jacuzzi. Also high on the list is being able to just hang out--maybe we run too much during the year, but they love grabbing a snack and relaxing. I end up cooking a lot of our meals--they prefer that to eating out.
Sorry for the book, I just wanted to give you some things to think about. Onsite can be great for some people. We found our joy offsite, after 5-6 onsite stays with children.