We've been waltzing etcetera since 1999. I play about half music for waltzing, half music for dances like nightclub 2-step, blues, rumba, cha-cha, foxtrot, fusion, swing… Personally I tango to most of it; other dancers do whatever they like.
My goal as DJ is to make the dancers happy. I watch the room, ferret out dancers' favorites, and customize my playlist to suit the dancers in the room right now. Exceptional music for dancing would be my claim to fame if I had any ;-).