We are a family of six, and are usually joined by my MIL, and we have stayed off-site (villa & Windsor Hills), WBC, and most recently on-site at POR. They all have their pros & cons for sure. We drive down, so transportation is a non-issue for us.
First, I feel confident that if we stay off-site again, it will be at WBC. The condos are so nice and spacious; the grounds and pool are beautiful; and despite the fact it isn't Disney property, I would argue it's pretty much in the bubble - just sans Disney theming.
Most recently, there were only five of us, so we were able to stay at POR (with the Murphy bed) for two nights. It was a wonderful stay! The resort itself offers so much to do, we could easily see how some people can spend time at WDW Resort and never go to the parks. We loved it!
BUT...
Typically when we go, we are there for 8 or 9 nights. No way would DH and I want to spend that many nights in the same room as our kids. Like some PPs have said, we like having space to spread out - especially after being around so many people at the parks!
So for us, I think where we stay will depend on the length of stay. And, we may even try an off/on property split stay next time.
Or maybe, if I wish upon a star, we'll be able to stay in a DVC 2BR for our next trip.