I thought for sure I had posted here before. I'd have to say waltz, just because the music has such versatility. It can be overjoyed, incredibly sad, and even furiously angry. There's such a range of expression in it that I don't quite see in the other dances.
If you are asking what my favorite dances are, I would say Bolero or Bachata.
Between the two, I have actually learned some Bachata and I have a club I can dance it at. My Bolero isnt really past the basic and fundamentals of technique.
Basically, Bolero (American Rhythm Ballroom style, I think) is my favorite in terms of beauty. Bachata is my favorite of dances that I am halfway comfortable with, although I do a modern style, not an authentic/Dominican style.
Now, if I were being hyper efficient, and the dance gods were really going to use magic powers to enforce the scenario, I would pick Hustle. I am semi-comfortable with Hustle, it is in my top 5 or so favorite dances (independent of my personal skill) and it can fit to most club, swing, chacha or merengue music. You can even fit it in over a Salsa with minimal stares from club-goers.