to be honest, I 've felt that Lex Luthor - much like Dr Doom- should be a really easy character to adapt to live-action, and also like Dr Doom, those adaptations have been pretty poor.
I enjoyed Hackman's Luthor, because he fit within the tone of the Reeve/Donner Superman films, but really he wasn't Lex Luthor in much more than name (and baldness).
I didn't actually care for Smallville much, but I did think they did justice to
Lex Luthor - so Rosenbaum gets my vote.
Oh, and Eisenberg, goes at the very bottom of my list - for what could have been an interesting "Alexander Luthor" interpretation, done really, really, really badly - in a confused mad scientist/Joker hybrid.
It didn't work at all, on any level. Which is sad because I beleive that Eisenberg has the acting chops - if they had taken his character from Now You See Me, and made him a bit more of an ******* that would have been
fine.
Sigh.