For years, and for many trips, we have used the WDW system for every - single - outing. We do drive to get the World, so we have our own car when we get there, but we have always preferred to park it, forget about it, and use the internal transportation to avoid having to drive ourselves.
However...
On the last couple of trips, we've experimented with driving ourselves and I must say, since we're finally empty nesters (just this year), it's pretty nice.
1. We get to the turnstiles, shows, and dining spots when we need to without having to leave so early from the resort.
2. We've never had to wait in line to leave the parking areas at the theme parks (Disney folk are masters at people moving).
3. We always have a place to sit down.
4. We don't have to stop at other places to drop off or pick up other people. 
On the downside, we don't meet as many folk and/or get to talk to people. One of our favorite things to do is strike up conversations with people and driving takes that away. Also, it's NOT worry free. I know, except for one time when a driver made an oops, that when I step on a Disney bus, boat, or monorail, that I will reach my destination and I don't have to do anything but enjoy the ride. Lastly, we've been known to enjoy a few libations while lounging at the pool at the resort, or while walking around the theme parks (except for MK); it's nice to know we always have a designated driver. Lastly, we will not drive to Magic Kingdom again... so much easier to use transportation than deal with parking and then ferrying or monorailing it over.
So, it depends on where we stay, what we're doing, how much time we need (or want to be lazy with) and how we feel at the moment with regards to if we drive or not.
In regards to resort selection:
Over the years, we've stayed at All Star Music, All Star Movies, and All Star Sports and we typically do Pop Century now when we need value if it's available BECAUSE it has a designated bus (All Star Sports is second choice because, even though it shares a bus with the other All Stars, it is first to pick up, usually ensuring a seat). We've done POR (when it was DxL) and POFQ because we love the boat ride to Downtown Disney, but the last few times, that has been very frustrating because of wait times; so much so that the boat is not a factor anymore for resort choice. What else, Coronado, Polynesian (most wonderful time ever), Yacht Club (nice pool), and Beach Club, the last being our current personal favorite with the short walk to Epcot and relaxing boat ride to DS.
In summary, proximity and ease of ingress/egress to parks via WDW's transportation is indeed our primary decision settler, even though we do drive from time to time now.
- Dan