To be honest, I think Tornadus should be B-Rank. I was using Tornadus the other day in UU and I was surprisingly disappointed in it. I was using the Acrobatics + Bulk Up set, and it really had some problems. The first move was pretty powerful, but after that, Tornadus just really didn't function as well. Flying STAB is invaluable in the metagame, but that doesn't help Torndus's main problems. First and foremost, Bulk Up is a pretty bad set up move when you are as frail as Tornadus - it wants something like Swords Dance. Its physical movepool is absolutely horrid too. Brick Break is not going to get past its resists, especially because it doesn't have a Life Orb attached. A Rain Dance set? I don't know, but it needs a turn of set-up to fire off accurate moves.