If you are going between DHS and Epcot Future World, there is bus service between DHS and the front entrance of Epcot. If you are going between DHS and the "right" half of Epcot World Showcase (basically anything from Japan to Canada) you are better off using the boat service between Epcot's IG and DHS (or walking). Anywhere else in World Showcase it's a long way to either exit, so pick your favorite.
Between AK and the MK there is bus service. On the MK end buses depart and arrive at the TTC, so a transfer to or from the bus to a monorail or the ferry boat is required. Another option for going between AK and the MK is bus between the CR and AK, with a short walk between the MK and CR. Downside of the latter option is the CR-AK bus likely will stop at one or more resorts coming and/or going.