MR from Smallville does the best Lex, partly due to talent, but mostly because his character is a 3-D representation. All of the films depict a Lex who is 2-D, not properly motivated, and not intelligent enough. I think we must also lay blame to improper direction, as these men probably wanted to infuse more into their characters considering past projects.
Lex from Smallville has been given a clear history and clear motivations regarding all of his actions. And its always more interesting to watch a character fall into darkness, rather than a character who has already fallen. I imagine, the creators of the series did read Lex Luthor: Man of Steel. (In fact, I cant wait to read it myself). I think Smallville really understood that for any actor to play the villain convincingly, that actor cannot see him/herself as evil or villainous. Itll never read on camera.
But its difficult to judge in the end, because Smallville is about Lexs downfall and Clarks rise to greatness. The Superman movies are about Superman and his journey. Lex is never really part of the story-line, not really, not enough.