Your options to the MK: Bus, car, taxi or monorail.
Your options to AK: Bus, car, taxi
We had very good luck with buses our last trip, they were pretty prompt, never more than a ten minute wait and we didn't have to stand once. But we've had worse luck on other trips, full of standing around for 30 minutes to catch a bus to get on one that was standing room, packed like sardines, with someone's stroller attacking your shins. Which is when we developed our affinity for taxis:
Taxis are going to add to the cost of your trip, but they are fast and efficient and always available at the front of the resort or the parks (out by the TTC at the MK). Talk to the bell stand and they will be able to tell you what the price should be and make sure you get into a Mears (Checker) cab. We've found ourselves saying we don't have time for the bus if we need to wait ten minutes - and grab a cab. Or saying we don't want to risk standing after a long day and grab a cab. A few cab rides a trip is still much cheaper than a rental car.
Rental Car: To us, this is a hassle, but a lot of people find the freedom of a car to be the ultimate in transportation.
Monorail: We often take the monorail back from the MK to BWV - the walk through Epcot is kind of long, but we see most of future world in "onesies/twosies" on our way through - or we pick up fastpasses for Test Track or Mission Space to use after a dinner and swim. In the morning, Epcot needs to be open to get to the monorail, so we've seldom done it that direction as we are usually at the MK at opening.