the best animes are those which are not that known in north america...
I'd say it's more that the best animes aren't known all that well anywhere.
I guess it's a little hard to put this argument across without sounding a bit elitist but I'm gonna try it anyway.
Most popular anime/manga aren't the most substantial works. Shonen and Shoujo tends to aim for the audience's preferences. Is that really an artistic way to approach things? Sure, you give the audience what they want but it kind of robs the work of individualised expression. Sienen's a bit better, since with it there's some recognition that an older audience might want more mature content, and in some works that only translates to more sex and blood, but at times more substantial storylines do come with them. However I'm of the view that the best works don't really give a damn about catering to a specific audience but instead follow and individual means of expression. Miyazaki's films are often this and it is why they are so popular but also highly acclaimed.
But for every Miyazaki there's dozens of talented artists and film-makers who can't really catch a break despite producing quality work.
All I can say really are the works that really made an impression on me. Le Chevalier D'eon Ghost in the Shell: Stand Alone Complex, Paranoia Agent. These are examples of works that are very well written. Far more complex than the likes of One Piece. Does that make them better? It's down to preference, in my view yes, but either way, no one can deny them being deeper, essentially.