Who’s more dominant: Sherlock, but it’s a well known fact that when Nick goes Grimm, he can be incredibly dangerous, and powerful.
Who’s the cuddler: Nick. He likes being touched and held, and while Sherlock does, too, he sometimes forgets that it’s important.
Who’s the big spoon/little spoon: Nick tends to be the big spoon just because he exceeds Sherlock in experience in that area. But Sherlock’s build is better suited to big spoon, so he sometimes does, too. Depends on how they fell asleep.
What’s their favourite non-sexual activity: They like staying in together doing whatever strikes them. Since both their jobs require them to be out a lot, they actively prefer being at the flat together like creepers and never going out socially.
Who uses the most hot water: Sherlock. His hygiene is important to him, and Nick is often forced to either shower with Sherlock, or take cold showers after him.
Most trivial thing they fight over: Music. Nick likes jazz, and Sherlock likes classical. Sometimes they get into spats over which should be played.
Who does the most cleaning: Nick. He has become accustomed to picking up Sherlock’s case files, or tea cups when they litter the entire sitting room.
Who has a season pass on their DVR/who controls the Netflix queue: Nick. He likes movies, so he likes Netflix. Sherlock hates the television.
Who calls up the super/landlord when the heat’s not working: Nick. Sherlock would really rather just curl up on the sofa next to Nick, suck up all his heat, and complain about it.
Who leaves their stuff around: Sherlock. Nick owned a house with his ex-girlfriend, so he tends to be a bit more conscious about his stuff lying around. Sherlock can’t be arsed.
Who remembers to buy the milk: Not Sherlock. (I’m seeing a pattern in his relationships…)
Who remembers anniversaries: Both of them. Sherlock because something important happened, and Nick because it is emotionally noteworthy.
Who cooks normally: Neither of them. Their schedules really don’t allow for much cooking.
How often do they fight: Almost never. They mesh very well.
What do they do when they’re away from each other: Both of them solve their respective cases. (Super detective husbands for the win)
Nicknames for each other: None. They aren’t really the nickname type.
Who is more likely to pay for dinner: Sherlock. He throws money at stuff for Nick like it’s his job.
Who steals the covers at night: Sherlock. Nick just steals them back, and laughs when Sherlock complains in his sleep.
What would they get each other for gifts: Nick would buy Sherlock something nice, and put a lot of thought into it. Sherlock would ask Nick what he wanted, and then go get it for him.
Who kissed who first: It was a mutual kiss situation.
Who made the first move: Technically Nick, although they both knew they had to do it.
Who remembers things: Definitely Sherlock, but only if he deems them important. Nick remembers everything he discards as pointless.
Who started the relationship: It was mutual.
Who cusses more: Probably Nick, although neither of them are terribly prone to swearing.
What would they do if the other was hurt: Find the person who hurt them. Proceed to make them pay in whatever way they saw fit.
Who is the dirty talker: Sherlock is likely more likely to, although Nick is one in his own way.
A head canon: The two of them go out together on weekends, and purposefully find crowded places where they can each use their respective skill. Nick identifies the Wesen, and Sherlock proceeds to deduce them. It is an incredibly entertaining experience for both of them.