I've had to narrow this down to two, because I can't separate them:
I've enjoyed Castiel's character development from the early days stoney-faced, smitey 'dick with wings' Castiel, to Dean's best friend and 'brother'. I've enjoyed Castiel's journey of learning about humanity and his many hilarious misunderstandings. I don't think Castiel's storyline has always been the best, and he's a character that's made some decisions and choices that I really haven't understood or agreed with, but on the whole, I have a very big soft spot for Castiel iand he's a character that I'd really miss
My lovable, grumpy crusty ol' codger. As salty as a bowl of pretzels but with a kind streak a mile wide. He was the father figure the boys needed so much, and when he said he 'adopted' two boys and they grew up heroes', I was snivelling like a pathetic snivelly thing!!