Favorite: The cats, Entei, Raikou, and Suicune, are my favorite trio. They have, by far, the best designs of the trios, and I have to vote for them as a cat lover.
Least: The Regis. They just look boring compared to the other trios, in my opinion.
Regis are my favorite, all three are favorites of mine, which isn't the case for any other trio.
The Lake Guardians would be my least favorite as I'm just not into the pixie concept. However, I have no real issue with them, and I do find them interesting in their own way. I don't dislike them at all.
They're all pretty unimpressive.
If they count, Groudon/Kyogre/Rayquaza
Least favourite are the Lake Guardians for all looking too similar.
Favorite: The Bird Trio
Least: Golem trio
But I just adore the Lunar Duo
Oh my Feebas !
Friend Safari Flying : Pidgey, Woobat, Rufflet.