Put us in the rental car / drive to the parks category. Having done visits both with and without a car, we always rent a car now. Our main reasons:
1. Getting to/from the parks is faster in our own car in most cases. If staying at a monorail resort, obviously monorail or boat is best to MK. But staying elsewhere on property, we find that it's a toss-up between bus or driving. (We actually split up once to test which method was fastest to MK and we all arrived within one minute of each other.)
2. Standing on a bus back to the resort at park closing that is packed with tired, grumpy, sweaty/stinky others is not our idea of a fun time on vacation.
3. Getting to/from dinner ADRs at resort hotels is far and away better if you have a car. Disney transportation is designed to get folks to/from theme parks, so travel between resort hotels on Disney transportation can take forever.