I can't believe I'm the only one that can answer "both!" :)
I'm a firm believer in discs. The day video games go digital-only is the day I become a book worm or something. Not a chance I'm downloading 80GB games.
BUT I started with Splatoon on disc, ended up with my present Splatoon addiction, and decided that I also wanted to play other games too without switching around so then I ALSO bought digital which installed right onto my existing save data and was seamlessly played as though I never removed the disc. Win-win I get my OCD stack of boxes AND the convenience of digital! :)