Driving to AK, DHS and Epcot is not bad. You park, walk or tram to the front gate and you are there. The buses pull up to a place where there is a shorter walk from the bus stops to the front gate, but the advantage is not that great.
If you drive to MK, however, you park, walk or tram to the TTC and then take a monorail or the ferry to the front gate. The buses, meanwhile, go right up to the front gate. Due to this extra step of monorail or ferry, when going to the MK, using Disney transportation can be more convenient than driving.
And, the Disney bus system is generally quite good. There are waits for buses and trying to get a bus at a very busy time (such as park closing time when everyone is leaving all at the same time) can take awhile. But, the system overall is very efficient. That doesn't mean there are not individual complaints that are justified, but for the most part those are the exception rather than the rule.