I'm not an expert but have some recent experience with the issue. When we were there in the middle of march the bus service was fine IMHO, you might be standing but we always fit. If you plan on getting to the parks at opening get to the bus stop at least 40 minutes ahead of park opening.Sometimes it will take 15-20 min for the bus to get there(if you just missed one),then about 10-15 min to get to MGM or AK.