There isn't a best in my opinion. Each anime has their pros and cons. I recommend DBZ, Naruto, Bleach, Fullmetal Alchemist and FmA Brotherhood, Sword Art Online, Death Note, Yu Yu Hakusho, Ruroni Kenshin, Akane Ga Kill, One Piece, Attack on Titan, and I'm sure there are plenty others I'm forgetting. But I'm sure the other posters will fill you in!