I don't know what you like, but personally, of the things on this list I'd skip the others and ONLY watch Kuroshitsuji...and now that you've edited it, I really don't know.

Clannad was a really sad and heartfelt I thought it was an amazing anime even though Kuroshitsuji and K-ON! are great too I suggest Clannad and Clannad After Story first but the choice is really up to you.

I CAN'T DECIDE! >< Watch all of them at onceQ!

one of the best anime ever! <3

Clannad may be a bit slow at the start but it's worth it once you make it to the end. <3

Thanks for you all to think of Black Butler because I LOVE that anime and because I've already seen it.... ^^"

Does not really matter which one you watch first. because the other one will still be waiting for you. However, I would watch Clannad first.

I haven't finished Clannad yet but K-on! is just AWESOME!!