Chris Evans has recently been given the role of Captain America and not that I think he can€™t do it, just, he is the Human Torch first in my mind. I thought it was excellent casting when they chose him for the role. He is too good of a Johnny Storm to switch to Steve Rogers. Rogers is All-American gentlemen and soldier while Chris Evans plays that smart-ass wise guy role of Johnny Storm so well that being in a born-leader role like Mr. Rogers seems like an ill fit.
I think Chris Pine (Captain Kirk in the most recent Star Trek movie) makes for a good young Captain America while also not messing with the current Marvel universe movie cast. He proves in Star Trek that he€™s young but still got the chops to be the leader and make important decisions. This is the man who you want leading The Avengers, not the fun, smart ass guy making jokes and showing his inexperience.
Read a little bit about the character to get the feel of who Steve Rogers/Captain America is. Check the Wikipedia page here or if you€™re looking for some great comic book material, look up Civil War, by the Mark Millar. (This guy who brought us Wanted [the comic is much better than the movie with Jolie], Old Man Logan, and the most recent comic book turned into film, KICK ASS, and his most recent comic book, Nemesis, first issue has just been released this month and I already got mine)
Side note: BHSC writer is a huge comic book fan, so expect more posts like this. If you don't like comic books/graphic novels, re-evaluate your life.