One Piece

[Proxyt]

To be the best you have to define what you're best at.

ie: What's the BEST song? What's the BEST book? Who's the BEST actor?
It's easier to classify best, or at least "top" picks if you use subcategories for such large collections such as "songs", "books", or in this case, "anime". It's also easier to have a certain rivals to compare them to.

Artwork? Not the best. (Clannad, Durarara...)
Music? Not the best. (Gintama, Hajime no Ippo...)
Plot? Pretty good, but I've seen better. (Code Geass, Cowboy Bebop...)

Pretty much every single of these common categories One Piece will lose, but it's definitely a great anime,

and One Piece is certainly the best anime at keeping me interested for so long. 300+ episodes long and even at episode 450 I'm still anticipating the next episode.

Most long animes get boring after maybe 50 episodes, but One Piece is one of the few that continue to captivate my attention for so long.