I've gone for Brandon Routh as Superman, Cain and Hatcher as Lois and Clark (of course), and Michael Rosenbaum as Luthor.
I chose Routh because he seems to do the sheer alienness and loneliness of Superman at least as well as the others, and the whole "this is someone who knows how to use his powers" thing that is largely down to CGI but still pretty impressive - scenes like the earthquake in Metropolis where he's handling dozens of different problems simultaneously, the moment when he's shot in the eye at point-blank range and doesn't even blink, and so forth. He isn't as physically impressive as Reeve, and lacks some of his presence, but it really works on the powers level.
I don't think I need to justify Cain and Hatcher, but their interaction is a joy compared to the others. Neither Reeve or Routh seems to be able to move beyond "country bumpkin" as Clark, and the Smallville guy is just too young - similarly the movie versions of Lois are too two-dimensional, and the Smallville one is a joke.
As for Lex, I've always had problem with the character as a monomaniacal villain, at least Smallville shows us someone who started out with good intentions and is slowly corrupted by wealth and power - Rosenbaum plays him as the most interesting character in the show, with the possible exception of Chloe (who ought to be Lois, damn it!).
