I don't think it's a matter of Ayumi liking Yoshio better. I just think Enrique is shy - he doesn't seem all that touchy feely to me and like he prefers to be off on his own. Yoshio is much more open and cuddly which is why Ayu interacts with him more.
And chan can be used for any sex so long as the person is a close friend. Ayu herself refers to Yoshio as Yo-chan.