Voted for RikoMaruMari but ChiKanan's my other favourite.
ChiKanan = RikoMaruMari > DiaRuby > YouHane.
ChiKanan's duet has always been at the top of my list, but RikoMaruMari's song has joined it. It's just so fun and catchy, and it's by three great vocalists. I'm just sad Maru only got one line (which couldn't be heard properly because of the loud instrumental) . DiaRuby's duet is really nice too, but YouHane... I'm still not a fan of it haha