Let's me just Copy and Paste what I said from the guys at the Reddit MCU site that I go to that asked this same exact question to make my Life easier, Aplogizes in advanced if it's looks ugly.

1. Natasha Romanoff: I'm sorry but the whole Super Solider thing in the comics is so lame and tiring since pretty much everyone in the Comics are super solider, It's makes much more sense for me for Natasha and the Other Widows to become what they are without the Serum.

2. Nick Fury Jr: Ditto from Nat on the whole Super Solider Serum thing.

3. Cassie Lang and Kate Bishop: Do I even needs to explain why the MCU Origin is so much better?

4. Tony Stark: Just Tony Stark in general, his personality is much better (they tried to make him into a serious character early in his run, look up some of the older Iron Man comics if you don't believe me)

5. Bucky Barnes; Why did they made him a kid in the comics lol?

1. Nick Fury, who went from a generic white soldier guy to a fully fleshed-out character who knows a lot, but not everything, which is a great trait. He also has a great moral compass, and great motivation.

2. Helmut Zemo, whose original comic origin was “SOMEONE HELP, THIS CHANDELIER IS GLUED TO MY FOREHEAD!”. I think his story worked a lot better when he was humanized in Civil War.

3. Bucky Barnes, because he was a kid for some reason.

4. Ava Starr, because of her believable motivations and (I’m sorry, I’m a VFX geek) her visual effects, they were incredible and I loved them.