Well, what a question! My "favourite" song tends to change on a weekly basis, and I keep my StreetSalsa profile updated to reflect the latest belter!
If I had to name an all-time favourite... That would be the salsa version of Valio La Pena by Marc Anthony.
There are also songs that I wouldn't necessarily love listening to, but LOVE to dance to. And it's amazing how a track might come on and I get a specific dancer in my mind!
Superstition (not a salsa song but great for dancing to) will have me making a beeline for Rosa or Allison. And I'll never forget the time This Is Not A Tango came on and I turned around to greet Hannah with "I NEED YOU FOR THIS!"
There's so much to make a good song. For me songs that really help me to "dick around" with my musicality are sure to be winners!