What is the rarest skin on league?

I was having a conversation with a few friends and we were debating over what the rarest skin on league is.

My top two choices for the rarest skins are:

http://image.noelshack.com/fichiers/2014/41/1412764660-alishopclear.png http://i.ebayimg.com/00/s/NzE0WDEyMDk=/z/0KMAAOSwe-FU~aCo/$_32.JPG

Also just as a side note, my friend said that they arnt the rarest skins because there is a guy in LoL who riot gifted a skin to and its like a one of kind type of skin. Personally I don't think its true but it would be really cool if it was.

Lets discuss it?