It depends on how you do your day, we personally split things up among different parks each day, so we hardly ever (one or twice) drive to a park. I agree that the LOCAL bus is a pain, it stops at 5 resorts and usually BWI is last or at least it seems that way.
For MK, depending on the time we walk through Epcot and take the monorail. the thing is we are frequent visitors and timeis not a concern for us.
Car is usually best for convience, but I do not like having to be bothered by driving whenI can let some else do it for me.