To get anywhere in WDW, follow their signs -- if the gps disagrees, it's lying.
We only use gps when we're lost outside WDW and need to find our way back, to get to the airport, or to find a particular store or restaurant. You should be able to type in the name of your hotel, different theme parks etc.
We use the WDW bus system exclusively for trips to MK -- we don't love Epcot so we get there by monorail from MK for part of a day. For DHS and AK we will only drive if we're going to be there at park opening and can walk to the gate rather than parking tram. If we're park hopping we use bus. We always have a car on our trip, and we've tried all the parks different ways -- bus wins because you don't have to wait for the parking tram at the end of the night. But we stay at a Value and they have better bus service since there is no alternate transportation to them.