Darth Vader or Anakin Skywalker?
Darth Vader at his prime as machine-man or
Anakin Skywalker at his prime before he became Darth Vader?
Personally I go for Darth Vader. As Anakin he had more speed and higher midichlorians, but he was not yet an experienced Jedi though he killed Dooku easy and was extremely powerful already.
As Darth Vader he was full experienced in the force and he got extra power from the dark side.