I’m so sorry this took me so long! I went to bed like 10 minutes before you asked! 

who’s the cuddler: Dean. He’s a hugger by nature, and when he’s most comfortable when he has Sam and Cas wrapped up together with him.
who makes the bed: Dean. Sam gets the corners wrong and Cas doesn’t care so it’s up to Dean.
who wakes up first:  Sam. He likes to exercise in the morning. Dean’s next, usually up to make coffee and breakfast and Cas eventually rolls out of bed last. 
who has the weird taste in music: Sam. He likes the weirdest stuff, 90% of which Dean has no patience for. 
who is more protective: Dean. It’s kind of ingrained into him to protect Sam, so when Cas was added to the mix it was natural to protect both of them. But of course, Cas is willing to do anything for Sam and Dean and Sam’s pretty damn scary when Dean or Cas need him.
who sings in the shower: Dean. And poorly. 
who cries during movies: Again, Dean. Though, there was the Steel Magnolias incident in which all three of them cried like babies. I suppose it depends on what they’re watching. 
who spends the most while out shopping: Cas. Sam and Dean never had a lot growing up so they’re pretty tight with their money (even if they don’t really have to worry about it). Cas is much more willing to buy them all things they want but don’t need. 
who kisses more roughly: Sam. He knows both Cas and Dean can take it, and he’s more than a little demanding at times. 
who is more dominate: Personality wise, it’s Dean. He’s louder and much brasher than either of them. In the bedroom, it’s Cas. He’s bossy. (Though there are times when Sam gives Cas a run for his money.)
gets jealous the most: It’s not that Cas is jealous, it’s just that he feels insecure a lot of the time. Sam and Dean are bonded in a way he’ll never hope to replicate with anyone. Sam sometimes gets a little jealous of how Dean and Cas always seem to be on the same wavelength even when they butt heads. Dean is a little jealous of all Sam and Cas have in common. (He did try to express interest, but some of the podcasts they listen to him make him want to tear his hair out.) 
one headcanon I have: I think one of my favorite headcanons/tropes is that Cas is the whole reason it happens. Like, Dean and Sam have had entirely unbrotherly feelings for each other for years, but they don’t say or do anything about it until Cas decides he’d like to sleep with both of them. So then it’s threesomes with strict “no touching” rules and then maybe coincidental touching is okay. And then, okay, it’s not really that bad if it’s just kissing, right? It’s just kissing. And well, if it’s DP it’s only coincidental that Dean and Sam’s dicks touch. Right? That’s not incest or bad, right? Then… well, maybe Dean can’t help it if Cas is giving him an order to touch Sam, right? He could say no but he maybe doesn’t want to. And then somehow Cas walks in one them making out in the kitchen with a smug as fuck smile. Then everyone’s happy! 
Sorry, that got NSFW. Ooops. 
nicknames: They’re not really “for” nicknames, just more snide terms of endearment. (”bitch” “jerk”) But I would bet that Dean only calls Cas “sunshine” when he’s being a grump and Cas usually enjoys calling Dean “asshole”. Sam doesn’t usually get passive aggressive nicknames thrown at him from Cas. 
my rating of the ship from 1-10: 10