Legendary Birds : Zapdos, Articuno, Moltres
Legendary Beasts : Entei, Suicune, Raikou
Legendary Golems : Regice, Registeel, Regirock
Weather trio : Rayquaza, Groudon, Kyogre
Lake guardians : Mesprit, Uxie, Azelf
Dragon trio : Dialga, Palkia, Giratina.

I like the Dragon trio the most

Same, dragon trio here xD

The dragon trio is a lot stronger than the other trios :3

I wanna see a battle between the weather trio and the dragon trio tho!

Dragon Trio

Am I the only one who like the Weather Trio?

I only like Rayquaza from the weather trio. Kyogre looks weird, and groudon doesn't appeal to me :S

I like the Legendary Dog Trio ^^
(Suicune, Entei, Raikou)

I adore the lake gaurdains! Though I also love the cute trio.
Cute trio: Celebi, Jurachi, Mew.

As much as I like Suicine I actually prefer the legendary birds.

I think it has something to do with the fact they came out first. Their like Mew, Mewtwo and Pikachu- everyone knows about them, the newer legendary ones though I tend to forget.

There are trios missing! I'll add them below.

Legend Trio: Ho-oh, Lugia, Mewtwo.
Cute Trio: Mew, Celebi, Jurachi.

Out of each trio I like Lake Gaurdains the best.
Than the Cute Trio.
I have faves in each trio though.

I love Suicune, but the Golems Are my Favorite 8D

I have to go with the legendary dogs since johto is my favorite region

Weather Trio