This is totally random, but as far as the JONAS (LA) X BTR crossover (either one, really) goes...
Macy's favorite of the btr boys is carlos, because sports, and also bc he's just fun to hang out with. macy seems normal and put together at first, but she loves physical activity, as we know from s1, and carlos (platonically) matches her freak in the places nick doesn't
Stella's favorite is...and isn't james. she's basically that post that's like "you're in his dms. i'm pissing him off, i'm ruining his day" but in the most convoluted way possible, they also, platonically, match each other's freak. all in all, stella would rather spend time with the other girls, and she obviously adores joe, bc he understands her thoroughly, but james is like...the opposite. they understand each other and fucking hate it.
Katie and Frankie deserve the most insane sublot that builds up over time, until their scheme eventually collides with the main plotline and wreaks absolute havoc. they're ten years old and evil geniuses with famous brothers, you know the two of them meeting will bite everyone in the ass in the end.
I do think Nick and Logan would get along, but the thing is, logan is a science and math nerd and nick is a writing and music nerd. they're slightly different species of nerd. but I think nick would get along best with logan and kendall, bc even though they can go off the deep end sometimes, they're easier to handle than carlos and james.
I'm gonna ramble about Kevin and Lucy again bc I want to. it's so hard for me to imagine lucy with like, any other guy, just bc james is clearly gay, and the subplot with her and kendall was a total mess since he hadn't broken up with jo first... Anyway, they're both rockstars, and Kevin had a lot of character development in s2. he's kind, responsible, ambitious, and Lucy is headstrong, confident, and clever. I feel like they'd actually have a very normal relationship timeline compared to a lot of other ships/couples, simply bc by the time they're both in the narrative they're 18/19 and living on their own.
Joe...he would get along best with kendall, not just for the main character energy, but also bc I feel like they react similarly in a lot of situations, but joe is also a little more self-sufficient than kendall is, which isn't a bad thing, and is mostly due to living in la without his parents for a/multiple (depends on crossover fic) summer(s), whereas kendall's always had his mom and friends doing everything together.
Kevin's an interesting one, bc while s1 era kevin would definitely be best friends with carlos, by the time jonas la rolls around he's mellowed out. he's still a little dramatic sometimes, but post-HMA Kevin is very different bc of the responsibility for his brothers he gained over the summer. I feel like he'd sort of keep that older brother role he's grown into, so, besides his relationship with lucy, he's mostly helping clean up the trouble and not cause it. at the same time though, i think he'd get wrapped up in the katie and frankie subplot the most
Joe and Camille would also get along pretty well, mostly bc they have acting in common, with joe wanting advice from camille solely due to her years of experience. she's also easier to talk to than bigger names in the industry, so it's more of leaning on a friend instead of a mentor
Jo and Macy definitely spar every so often, mostly bc jo likes that there's another girl around that she can connect with about physical sports. it's not the same trying to spar with kendall, and now she has someone who's an even match against her.
Mona is one of the few people that aren't afraid to go toe to toe against griffin, given she doesn't work for him, and she's definitely screamed at him for Kelly's sake. gustavo is a little afraid of mona, and rightfully so. she's proud of that.
Still no one likes DZ