Jonouchi/Joey is my number one favorite in the original series an Duel Monsters! but I also like Kotori/Tori in Zexal,Luna/Luca in 5D's and Asuka/Alexis in GX.
I love Kaiba. Like, even though he is a complete biatch to Yugi, he is such an awesome guy. Like, season 2, Mokuba is trying to stop a bully in the battle city tournament from taking TWO rare cards. like, the dialouge legit goes like this;
Mokuba: I am the commissioner, and what I say goes! So leave that kid alone and scram.
Bully: or what?
Kaiba (who we all know is going to be standing right behind the bully): Or you'll have to deal with me.
See? Total boss!