I would agree that Winter Soldier is one of the better MCU movies. More importantly, I would strongly recommend watching it if you are going to watch Civil War. It really sets up a lot of what happens in Civil War.I've seen Infinity War, but don't recall a Wanda or Vision! They must have had small parts.
Always heard Ultron was the weakest, so never tried to watch it. I did see the first Avengers. I think Ultron came out after Iron Man III, which was so bad, that I didn't trust it. Same with Winter Solider (generally considered weak)(I have seen First Avenger and I do want to see Civil War).
I really should have watched Endgame by now, but wanted to watch Captain Marvel first. I'll do it this weekend.