Does it really have to be one? I have several that are tied for top spot.
In no particular order:
Iron Man 1
Iron Man 2 (iron man 3 got kind of stupid)
Armageddon
Independence Day (Can't wait for the new one to come out)
Star Trek (pretty much all of them were top notch movies)
Forrest Gump
Cast Away
Shawshank Redemption
Django Unchained
Gravity
National Treasure (both 1 and 2)
Unbroken
Oblivion
Paul (funny stuff there)
Pearl Harbor
Rocky (1, 2, 3 and even 4) After that they got stupid.
Green Mile
Oh man,, there's so many really really good movies. Unfortunately, Hollywood is starting to run out of original or even semi-original ideas. Everything seems to be going to remakes now. The new Superman movie "Man of Steel" was pretty good too.
I'd also have to say that when I see Tom Hanks in a movie, I don't even bother to look at the synopsis, I just get it and watch it. He's probably one of the greatest actors of our time.