Favorite characters aside from Hachiman?
Mine are:
Iroha - I like how she developed from Hachiman's presence in her life and turned out to be such a likable character lately. Although, her presence has some effects on Hachiman himself, too, which is nice.
Hayama - I like him for the fact that he's really so mysterious and is constantly stressed out that there's something wrong with him. For an example, the fact that he wishes for a fabricated reality as a way to cope with fact that he doesn't understand how to react to others' feelings and wants to avoid them altogether is obviously connected to the fact that he constantly stresses out that he isn't the nice guy everyone believes him, too. I also like the fact that he is basically the reason for the storyline in Oregairu, i.e. Yukino's mindstate and situation as well as the fact that he has so much parallels and dualism with Hachiman and is basically the opposite of Hachiman.
Haruno - Another mysterious and antagonistic character. She is too complicated for you to understand her from an outside point of view. And her facade is something that she doesn't even bother to hide once someone sees through it. In fact, she is probably the most manipulative and antagonistic figure in Yukino's life aside from Hayama. She gives off the feel that she is even more antagonistic and manipulative than Yukimum.
Haruno and Hayama are just so mysterous and affect the plot in such a heavy manner, can't help myself but to like them.