Ugh, I never noticed that I'm not really a fan of any of the 580 trios until now.
I suppose I'll say the Legendary beasts because Suicune is my 2nd favorite legendary, and I'm okay with Entei and Raikou. Plus I'm a big fan of their roaming mechanism. The feeling of excitement you got when you just stumbled upon one is amazing.
Hate the Kami's, the Regi's and Lake Guardians are meh, not a fan of the Fighting type, and while I like Articuno, Moltres's worthlessness in gen 1 w/o TM's keeps me from saying the birds are my favorite.
Not changing this sig until we get a new main series Tales game released on a Nintendo console in the US