In your opinion, have you ever seen an anime that has just worked well on all levels, everything coming together exactly as you want, and has moved and compelled you so deeply that you would call it the 'perfect' anime?
Don't be shy to say what it is, it can be any one you want!
For me, I choose the anime Elfen Lied. It is indescribable how this anime makes me feel, and I connect with it on so many levels that for me, I would call it my 'perfect' anime.