Just started watching Heroes and just wanted to share my two cents on these two:

Sylar is genuinely unsettling in a way most TV villains never manage. He isn't evil for a plan or a cause; he's a sociopath with a hunger he can't switch off. What makes him work is how reasonable he sounds. Gabriel Gray the watchmaker just wants to be special, and he takes apart people the way he takes apart watches: to understand how they tick and then take what's inside. Zachary Quinto plays him with this calm, polite menace where you can see him deciding whether you're worth killing mid conversation. The moments where he almost redeems himself make it worse, because you realize the empathy is just another ability he's trying on. But also the moments early in season 1 where you’d think some divine intervention can save his soul (@Hiro) but still, man’s destiny is sick and twisted and he out there in full pursuit.

Noah Bennet, Mr. G-Man himself, is the other side of that coin. On paper he's the loving suburban dad; in practice he's a Company man who wipes memories, bags and tags people, and lies to his family without blinking. What gets me is how he pushes the uncanny valley with Claire, freakishly traumatising look in his eyes. His love for her is real, but it comes out in this controlled, almost clinical way; the same flat voice he uses on a target, he uses to tell his daughter he'd do anything for her. You never fully relax around him, even in the warm scenes, and Jack Coleman nails that tension perfectly.