Destiel, Destiel, DESTIEL.
shops for groceries: Both. And it takes them fucking hours, because Cas insists on inspecting each and every piece of fruit before he picks one. Sam refuses to go shopping with them since The Incident With All The Blueberries (“We can never go to that Piggly Wiggly again, Dean!”)
kills the spiders: Neither. Cas refuses to kill any insect (except parasites, Dean’s seen him sit for hours picking every flea and tick off a stray dog). He’ll chase bugs around the bunker with a cup and a paper plate (both carefully labeled ‘FOR CATCHING BUGS’), attempting to reason with them that this is not the place for small insects, they will not be happy here, tells them not to be afraid, Cas promises to find them the best tree to live on/rock to live under. Dean doesn’t want Cas to look at him with the face Cas would look at him with if he ever did kill a spider, so he never does. Cas named the large orb-weaver that likes to build giant hobbit-death traps just outside the bunker hatch Abigail.
comes home drunk at 3am: Neither. They’re responsible adults, these days they get drunk at home, when drinking needs to be done. Besides, Cas is an affectionate drunk, and he doesn’t want to have to worry about some foolish human who thinks God cares about sexual orientation when God doesn’t even care about the apocalypse, Cas just wants to sit in Dean’s lap and tell him what a good person he is and look at his freckles really close.
makes breakfast: DEAN. Because he likes it, he knows how, and Cas is a giant Mister Grumpypants in the morning. Dean swears he hisses at him in the morning, like a big angry kitty, but Cas insists it’s Enochian.
remembers to feed the fish: They both do, Doctor Fishopolis and Ouestucati (“My sister, she was the angel of the sea wind”) are their responsibility. However only Cas takes them for walks.
decorates the apartment: Cas. Mostly because it scares Dean too much to think of one place as home enough to buy shit for, but also because Cas has terrible taste, and watching Sam try to hide his bitchface when Cas brings home a pink seashell windchime (“What wind is that gonna chime in, Dean, bunkers have no windows!”) or an old ashtray with a pin-up girl in the middle (“We don’t smoke, Dean, it’s just a bowl with tits on it!”) or another bag full of throw pillows (“Is he building a nest?! Is this like an angel thing?”) is usually the highlight of Dean’s week.
initiates duets: DEAN. He was half-expecting the angel to sound like an actual angel (or at least like, Freddie Mercury), but turns out shoving a Chrysler-building sized wavelength of celestial intent that still somehow had four very-unwavelengthy animal heads into one compact Midwestern vessel causes a bit of degradation in sound quality (but not, as it turns out, enthusiasm).
falls asleep first: whoever is the little spoon that night.