PDA?
Tony:
Tony Stark, being Tony Stark LOVES PDA. Especially at his famous parties, he loves showing you off and showing people that you belong to him.
Steve:
Steve being old fashioned isn't really one for PDA. The only thing he really can handle is hand holding, UNLESS someone flirts with you (but that's a different story.)
Bruce:
Bruce is okay with hugging and hand holding. He doesn't want to be too clingy, since he's afraid that you will leave him.
Clint:
Clint likes PDA, hand holding, hugging, and kissing ALL of it. Especially because you get flirted on a lot at SHIELD.
Thor:
On Asgard PDA is a normality, so he always holds your hand every time you leave the house.
Natasha:
Nope, the whole "Love is for children" and having her protective shield up all the time makes PDA a no no; SO she isn't usually up for it. Only hand holding sometimes, sometimes.