If I had to choose, I'd pick either the top left or the middle left. Don't like the font on the top left one, and the middle left needs something graphic like the umbrellas along with it. I think the top right one can be too easily confused for "fort walton" instead of "south walton".
Why don't you just sell them the SoWal logo? Or license them to use it? It's simple, compact, distinctive, and seems to be gaining traction.
After all these years, VRBO still refers to the area as "The Beaches of South Walton", not "South Walton." Tripadvisor doesn't even have a forum category for the area between Destin and PCB but lists the beach neighborhoods separately (seagrove, seaside, etc.). A search for "South Walton" on wikipedia brings up a disambiguation page for "Walton Beach", whose first reference is "Fort Walton Beach", with a secondary reference to "The beaches of Walton County, Florida on the Emerald Coast." I won't mention the confusion with Santa Rosa Beach and Santa Rosa county.
http://en.wikipedia.org/wiki/South_Walton
If I were in marketing I'd try doing something with all three sites to try to ensure South Walton points first to South Walton.