Great thread, I personally like Tennis the most, most fun in multiplayer. But all are pretty fun, except Baseball, which was pretty boring. Boxing was a surprising good workout. Maybe I should get Fitness boxing, not in a good shape currently.
A similar poll for Wii Sports Resort would be interesting as well, although it has more than 10 options. Archery and Sword fighting were pretty fun there, while flying around the island was great as relaxation.
And we need Switch Sports soon.