Rayquaza.
Why?
some years ago:
I was playing Sapphire and i found a way to get to a place where i never came befor, that was the where rayquaza was.(forgot the name ) I liked this pokémon so much that i started to train it, it became the best pokémon of my team(in Sapphire)
and now:
He is always in my team that i use for the league and to train other pokémon.