I feel like almost every major Marvel character has been shipped with everyone else at this point, it’s kind of hilarious. The classic ones are everywhere—Steve/Tony, Peter Parker/MJ, Wanda/Vision. But the real fun is in the weirder pairings. I stumbled into a bunch of Steve Rogers/Bucky Barnes fics after 'The Winter Soldier', and some of those AUs where they’re just two guys running a bookstore in Brooklyn are weirdly sweet. Also, anything with Loki tends to go off the rails romantically, from dark throne-room power plays to coffee shop meet-cutes. It’s less about the heroics and more about the emotional scaffolding the writers build around a single look or line from the movies.
Honestly, I gravitate towards the ones that aren’t canon. There’s a whole subset of ‘Peter Parker & Harley Keener’ imagines that bloomed from like two seconds of screen time in 'Endgame'. The appeal is filling in the gaps, you know? Someone takes a hero, strips away the suit, and asks what makes them tick when they’re just trying to order pizza or fix a sink. The romantic plots work because the foundation of caring—or angst, or mutual pining—is already baked into these characters saving each other’s lives all the time.