Based on my experience with films, and inspired by this man, 3 Great Actors in No Particular Order

1. Anthony Hopkins- Hopkins is an actor who excels at playing very intelligent characters, from the polymath Charles Morse in The Edge to the chilling Hannibal Lecter of The Silence of the Lambs to C.S. Lewis in Shadowlands, with depth and nuance. He has great range, and is a true pleasure to watch.
Best Performance- Hannibal Lecter, The Silence of the Lambs. A classically disturbing performance, perhaps the greatest villain in any film I've seen.

2. Peter Sellers- I must admit that I haven't seen a lot of Mr. Sellers (a few Pink Panther movies, Being There and Dr. Strangelove). However, I don't think any modern comedic actor comes close to reaching his level. He can play any character, no matter how strange, and somehow make them authentic and hilarious.
Best Performance(s)- Group Captain Lionel Mandrake/President Merkin Muffley/Dr. Strangelove in Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb. Three diverse characters, all hilarious.

3. Al Pacino- Mr. Pacino played a lot of dangerous characters, from Michael Corleone in the Godfather Trilogy to Tony Montana in Scarface to Lefty in Donnie Brasco. He does it perfectly. There is something about his cool performances which suddenly and passionately erupt rhat creates an impressive aura of menace.
Best Performance- Michael Corleone in The Godfather. His descent from being a fine, upstanding war hero to a cold, calculated crimeboss is convincing and frightening.