HANDS DOWN IT'S C-89.5 SEATTLE
They've been programming a Mainstream Dance format since the early 90s! They never bailed on the format, never leaned Hip Hop, and always played lots of new Dance music.
C-89.5 has a professional CHR presentation despite being a High School station, it has a good signal for the Seattle-Tacoma market, and it has many great specialty shows that start at 8 or 9 (instead of at midnight).
One of the reasons Seattle's got such a great club scene, and just about every major DJ/act plays there, is b/c Seattle has this Mainstream Dance gem on FM to expose Dance properly to the masses.
Seattle radio in general is amongst the best in the world bar none, with just about every format represented on the FM dial.
Anyways, my vote undeniably goes to KNHC.