If we get a SM character cameo in a post-SM special episode, I hope we'll see Lilie since she's the only cast member who I think deserves an expanded role given that she was so important in the games. And I may be alone in thinking this way, but she's always seemed like Satoshi's main SM companion to me.
I'd say the guys compete as Ash's closest companions this series, especially Kiawe, but I do think Lillie's had some of the most intimate moments with Ash in SM, especially the AF arc.