I have a little list. It's impossible to single out one favourite Rioter, but I've narrowed it down for the time being.
Xypherous (He gave the gift that keeps on giving--Orianna. <3 )
IronStylus (Who DOESN'T love that whacky parrot?)
Ezreal (His @Ezreal thread is one of my favourite haunting threads. Also designed my fave champs outside of Xypherous'. Can these two team up nao?)
Bok (The only Rioter I've gotten to play with, and he's magnificent! Anyone who will answer my silly questions about favourite colours or kitchen utensils in all seriousness before lobbing a Nid spear at me is made of win.)