Myth, Snob and Tiger Tiger... but only because I haven't tried that many yet! I'm sure it will change next weeK! I just bought a red one, ruby woo to try the Gwen look and I saw polietly pink and thought it was gorgeous too! But Snob is my most used one!
My top three in no particular order:
Viva Glam V (my first MAC lipstick, looks great with a smoky eye)
Viva Glam VI
Varneesh (it's a lip laquer which is considered a lipstick, it's my HG)
Honorable Mention:
Craving (looks bold on me without being to loud, love it)