Welles was a definite visionary with a keen eye for creating memorable shots. He created a couple of masterpieces, some good but flawed films, and some not so good films, but even the films that don't really work are still interesting from a construction standpoint. He was a master filmmaker and a true auteur.
Murnau's films, particularly Sunrise and Nosferatu, are the ones that really sparked my interest in silent films. He was a graceful filmmaker who told stories in such a visually powerful way that you don't even notice that there's no sound.
How do I love Fellini? Let me count the ways: La Dolce Vita, Nights of Cabiria, La Strada, 8 1/2, the list goes on and on. A one of a kind filmmaker for whom a word ("Felliniesque") had to be invented in order to properly describe his work.
Is there anything Billy Wilder couldn't do? Drama, comedy, noir, the man could work with just about any genre and produce a film that would become one of its defining examples. To have Sunset Boulevard, The Apartment, Double Indemnity and Some Like It Hot to your credit would be enough for most filmmakers, but he's also got Sabrina, Stalag 17, Ace In The Hole, Witness For The Prosecution, and The Lost Weekend.
A true master. No one has ever known how to do suspense quite like him and his best films have more than withstood the test of time, many of them becoming part of the collective consciousness. My personal favourite is Rear Window... no, Psycho... no, North By Northwest... nevermind, I can't choose. He was the best, I tell ya!