For 4 adults, I'd choose the Swan. It's location has so much more to offer than that of the WL. You can walk (or boat) to two major parks (EPCOT & MGM) as well as the Boardwalk entertainment area. There are many more restaurant choices in the area, too.
The WL is certainly a wonderfully themed resort, but unless you plan to drive everywhere, transportation is not as convenient. Other than the boat to the MK (which makes stops at the Ft. Wilderness campground), you'll need to ride the buses.
In my experience, adults who have never been to WDW tend to imagine it as a giant amusement park for kids - i.e., the Magic Kingdom. Wouldn't it be great to show them what a wide variety of entertainment options WDW has beyond that? I think the EPCOT resort area is a perfect showcase for adults making their first trip! JMHO. YMMV.