That depends on where you are staying and what time you plan to arrive at the parks. For example, if you are staying at AKL, then when you go to AK you might take the bus. But to all of the other parks it would be easier to drive. If you are staying at Wilderness Lodge, take the boat to the MK, but drive to the other parks. You can really just play it by ear and see what you prefer. If you're going when it's busy, you might prefer to drive than deal with crowded buses. If you're going to have strollers, you might find it easier to drive than to haul them onto buses. Really depends on your situation.
We always arrive at the parks before rope drop, so we are able to walk from the parking lot without taking the tram. Like others have said, at MK this requires parking at the TTC and taking the monorail or boat. But as long as we are there before rd, this is part of the fun!
We've also found that if we are staying at a park until closing, it is faster for us to drive than to wait for buses with a gazillion other people.