From the main cast I go with Yui, just love that kind of characters (some highlights are her poker face and how she likes the jokes of Ayano ... which in season 1 was my favorite character, but surely is not getting enough screen time in season 2).
I would choose Akaza Akari, because she... haaah i can't describe her with write, i just can described her with my feeling,and i really hope that God create a girl like her. And i will always acknowledge her presence even she's not at beside me :D ;D
But really I love basically every character in Yuru Yuri, including scary Chinatsu. At first I thought she was a b*tch but there's something about her I really like now. Plus gags that involve her being terrifying / creepy are cool.