Tony- Dancing. Strange enough its not the risque moves he likes, but rather the innocent spinning in a circle, air guitar and just jumping around the room type of dancing that he likes to watch you do.
Clint- Play video games. Unlike most people, who get extremely into a game, you remain emotionless when you play. Clint finds that funny because you're usually pretty easily worked up IRL, but when you're gaming nothing bothers you.
Bruce- Science. He loves it when you work with him because you always hum as you work and he thinks the that the way your face will scrunch up when you concentrate is very attractive.
Steve- Read. He likes how you get really into a book and he can always tell what type of scene you're reading by the emotions on your face. He thinks its cute.
Thor- Cooking. He finds the way your eyes light up when you cook absolutely adorable. It also helps that he gets to eat what you make.
Loki- Play chess. You don't really know how to play chess so you usually just wind up playing castle invasion with the pieces. Sometimes you can even talk Loki into playing with you.

Pietro- Use your powers. He likes the way your face scrunches up when you concentrate and he may like to try and cause you to mess up so that you'll put your hands on your hips.
I sat down to write a preference about your first fight and boom two ideas come at once. I have a love-hate relationship with my brain sometimes. Does this happen to anybody else?