It... doesn't make a big difference to me. [Even if he gets uncomfortable on the kitchen chair, he can just temporarily disable the sensation of it. And the couch would carry the risk of leaning in a way that prevent healthy ventilation. But if Sans is suggesting it, then maybe he wants the excuse...?] But it is sturdier seating. Better if something surprising happens. Yeah, let's go.
papyrus doesn't care, but any sad couch icons would be more relevant there