There is only 1 fact which is Iroha is the best girl and lives up to 8mans expectations. Yukina is just too cold hearted and her personality is jsut plain jane. Yui is more lively BUT that is not her true side as she could be the same as Yukina cold hearted.
Then we have Iroha, always cheerful and sly but still she is happy and being honest so Iroha WINS.