Hello there! Other of my thoughts about them. I'm open to debate on this as well.
Brooke/Kelso:
Gives nose/forehead kisses: Brooke, consistently gives him kisses on the nose/forehead even eyes on Michael after reproaching him about chaotic of his “mastermind” plan.
Gets jealous the most: Michael
Picks the other up from the bar when they’re too drunk to drive: Brooke
Takes care of on sick days: Brooke
Drags the other person out into the water on beach day: Michael
Gives unprompted massages: Brooke
Drives/rides shotgun: Michael drives and Brooke rides shotgun to make sure he's not distracted by toy stores to buy their kids or himself.
Brings the other lunch at work: Both, it's already under evidence that both of them showed up at each other work. (Pretend that he did not work as security at Playboy Mansion)
Has better parental relationship: Brooke
Tries to start role-playing in bed: Okay, mostly likely Michael. Same time, I do kind of feel like Brooke would do that since she is a bookworm. Perhaps she would read the smut/spicy book to him.
Embarrassingly drunk dancer: Michael
Still cries watching Titanic: Brooke
Firmly believes in couples costumes: Michael
Breaks the expensive gift rule during Christmas: Michael
Makes the other eat breakfast: Brooke
Remembers anniversaries: both, I mean Michael might be a moron but hella good at remembering. I bet when their 40th anniversary, he would told her the color she wore the dress back first time they met at the Molly Hatchet concert.
Brings up having kids: In canon, it was just an accident that happened to have a baby together. Michael would more likely first person bring up having kids with her again.
Besides my “Mike is a foster kid” theory; I don’t really care if Mike in the movie is an Afton because it sort of still pushes that idea that in more than one universe— regardless whether he is related to William or not, whether it is the smallest inconvenience to the biggest fuckup…
THERE IS SEEMINGLY ALWAYS A MICHAEL to put a massive roadblock or a tiny wedge into William’s shit and I think that’s hilarious.