Well, it kinda depends on what you mean by "Best". I class Anime in two different ways, Nostalgic and ones I've discovered as I got older.
You can also argue the type of anime, both genre and target audience play a role into what Anime you like too. For example I like Shojo (young girl) anime like Cardcaptors and Sailor Moon as well as Shonen (young males) anime such as One Piece, Bleach and lesser known ones such as Blue Exorcist and Beet the Vandal Buster.
Nostalgic anime for me, are ones like Cardcaptors, Pokemon, Digimon and the shows that were on Toonami, like Dragonball, Ultimate Muscle. While I still like some of these anime greatly, my taste has expanded into new animes.
Such as : Haruhi Suzimiya, Lucky Star, Fruits Basket.
But the best anime are still the ones from my childhood as I held them with such fondness and childhood innocence, mostly Cardcaptors. Which had a really really bad dubbing with a great theme but I still watch the new Animes too so there a sort of balance between my choices.
In Conclusion, Cardcaptors, Fruits Basket, Haruhi, Blue Exorcist are my favourites and be the ones, I'd recommend to anime fans.