DAMN IT, THIS IS HARD TO ANSWER!
Will just stick to ONE PIECE since it's really good.
But I have hell load of runner-ups... won't mention them because I'll think I've betrayed them. wwww
Besides, without being biased to the seiyuu and the songs, the plot is really magnificent. Though this series is really long and I think ENDLESS, I've enjoyed every bit of this. The art is so-so for me, yet I can't deny the fact that this ordinary adventure anime caught me off guard.