My personal experience has been that, in general from most any resort, Disney will get you to/from MK a little faster. Your car will get you to/from the other parks a little bit faster. Your car will get you to/from other resorts a lot faster.
As for which way to go---the time difference is modest either way, so it's really down to personal preference. What sounds like more of a vacation: never having to grab your car keys, or never wondering when the bus will come?
I'm normally pretty Type-A about these things, but we passed on the car on our most recent no-kids trip. I found the bus system from OKW to be more pleasant than I expected. We'll probably continue to rent a car when we bring the kids, but if it were just the two of us, we could be happy without the car.
Either way, I'll probably not take ME back to the airport again. The trip to the resort was okay, but the trip back was pretty unpleasant---a bus full of tired, sunburned, dehydrated people leaving the World for the real world. Blech!