I've been a fan of Dicaprio's since Man In The Iron Mask. Silly as the movie is, it's fun, and he plays both the arrogant king and the humble Phillipe. When you can play two polar opposite characters convincingly in the same film, you get my respect.
But he's not Captain America.
Brad Pitt would be my choice for Cap.... five to eight years ago. But yeah, he's showing his age nowadays.
Oh, and as far as Malkovich, you'd never get him. He views comic book movies as beneath him. He was offered the Norman Osbourn role before Dafoe, but turned it down because "I don't do genre work".