I won't say best, because, well, you know...arrogance. But, favorite's alright. These are just mine, they speak for no one else. I do invite others to put theirs up.
3:10 To Yuma
No Country For Old Men
There Will Be Blood
Margot At The Wedding
[ed: here's five more, FROM THE FUTURE!!!!! Now it's an even ten]
The Assassination of Jesse James by the Coward Robert Ford
Sweeney Todd: The Demon Barber of Fleet Street
The Diving Bell & The Butterfly
4 Months, 3 Weeks & 2 Days
The strength of the writing, atmospherics, cinematography, music, performances, directing, style, effects, and production and sound design make these films pretty amazing works of art. All but No Country are criminally underrated and all of them have the same qualities as some of my all-time favorite films. They make such precise choices in their construction and are masterfully crafted by people with brilliant minds.