Yondu's death is up there for sure. That line about Ego being his father but not his "daddy" was fantastic.
But as far as my favorite emotional moment in MCU. I think the Steve and Bucky fight at the end of WS is still the best. I'm just a sucker for when these films cram huge emotional character moments in the midst of chaos (usually the 3rd act).
It's usually the best superhero films that pull it off.
https://www.youtube.com/watch?v=c-U-x-okaXA
Cap was betting his life on Bucky remembering him. That's some shit right there. Said so much about his character, and I still feel like the moment is a tad bit overlooked.
It's a bit tropey though? (I realise most things are). The 'appeal to love/emotion to break through brainwashing/memory loss'