Yes, it certanly is the best. Sopranos not far behind and Game of Thrones catching up, but the Wire is actually a piece of art and not only entertainment. It grows from beeing a criminal series to become a series showing the decay of a whole society and complex problems with no solutions at sight.
I think Boardwalk Empire has really come into its own now too. It is pure pulp, but it is just so handsome and authentic. Plus, it has populated its world in a way comparable to The Wire.