We stay at the WL quite often and always (well almost) use the WDW transportation. Its about a 10 minute boat ride to the MK. You can get the monorail to EPCOT just outside the gate. The bus to EPCOT, MGM and AK take longer, but the ride is not that bad...15 minutes or so. The hard part comes with waiting for the boat and bus. You never know if you've just missed one or not. :lol:
Our kids are older now, but the only time we used our car was when we were staying out late. If you plan on staying until the parks close then you may have to wait for an empty boat or bus. It was just easier for us to drive.
What park are you planning on spending the most time in? That is a big factor for us. When the kids were small it was the MK so the Contemporaty, the Polynesian & the WL were our choices. Since they are older and we spend more time in EPCOT and AK we have started to stay elsewhere. This past year we stayed at the Boardwalk Inn... very good location. Walk to EPCOT, short boat ride to MGM and then bus to AK & MK.
Don't forget about afternoon breaks; they always help when you have kids, especially in the hot weather.