I've always bought physical, but for the Switch, I'm definitely going to go for Digital.
Carrying a case of games around is a risky hassle that's generally not worth the headache of switching out if I want to play something else.
If Switch were a home-only console, I'd buy it physical purely to stare at that boxart on my shelf knowing that all my games are safely stored in my home, but seeing as I take my Switch out and about, the benefit of always having Smash ready to fire up, not needing a physical cartridge to operate, and never being able to be lost definitely outweighs that purdy box.