First, some people need to learn to use the spoiler tag if it spoils anything of a manga. Even by saying "best girl won" it ruins a romance title.
To be fair, Itsuki grill was the first grill he met (can better say first grill that shows up in the story). If i learned anything... that usually means that person has a high chance of winning. While i do like Miku, i somehow dont mind Itsuki.. well guess at this moment im just not a fan of Nino.