That one piece opening was excellent, thank you. I won't know it if I don't come here because while I like One Piece, I never watched the anime
(the amount of episode is just...too big).
As for the best OP....Yakusoku no Basho e of Kaleido star and Hajimari no Kaze from Saiunkoku no Monogatari. Both songs have an irreplaceable place in my heart ;_;
Hajimari no Kaze - Saiunkoku Monogatari :
http://www.youtube.com/watch?v=ivsqb4jZNas