If the Weyoun character seen in "Treachery, Faith and the Great River" survived and done further episodes, then I'd vote for that. The other clones were such slimey lackeys however cheerful, pretty much unredeemable puppets.
Jeffrey Combs did such a fantastic job with Shran though. His inability to accept being indebted to anyone. Invariably showing up at the last minute, Han Solo-style to save the day or otherwise having that last minute change of heart. Obeying his own codes of honor but not above torture to get vital information. Watching him do the unacceptable passed by without question, while a desperate Archer was uncomfortably too close to home.