before i start... i would like to correct0n1-suka... the specialty of water is not ice (they can control ice, water, and steam even without the presence of the blue moon... episode 9, i think, of book 3 entitled "the puppetmaster" shows that the specialty of water is blood-bending, which can only be done during the full moon, and not ice.
i believe that with this kind of thing, it is with respect to other benders... it contains within it the element of relativity, so i don't think we can be able to ideally identify what an ideal specialty is...
my friends and i would like to think of something similar to blood bending... haha... i t would be that an airbender can force out of a person's lungs air causing the person to suffocate... haha.
but then again, i believe any bender can do that... make a vacuum of sorts...
oh yeah... to add, i believe the avatar cannot master any single element, and i mean the "ultimate" of any single elements, kind of like a jack of all trades but a master of none... i think that no avatar can gain blood-bending, metal-bending, and lightning-bending... i mean, that would somehow keeo the balance of the 4 elements within the avatar... sort of a check and balance system...

