Given Mesprit is the only one there who is specifically linked to emotion, its kind of weird to call them the emotion trio, especially when fan convention has just been Lake trio.
1. Beast Trio
2. Tie between Muskideers and Kami trio
Muskideers and Kami have interesting stories, they may overtake Beast Trio if they get expanded in future games.
Being told that the Beast Trio was created by Ho-Oh isn't any more of a story of Moltres heralding spring time, Zapdos being used as an explanation to thunderstorms, and Articuno bringing winter. I also don't see how mythology takes away the mystery of anything when their stories often raise more questions.