Sylar's been through two different Claires at DDD. The first was from Volume 5, and was generally tolerant of him out of fear and the thought he was dead. And because he thought he was her uncle at the time, he tried to be nicer to her and defined his emotions for her in a more familial way. Then he canon jumped, and a new Claire from late Volume 4 came. He realizes that she is different, and throws her hatred of him back in her face in his usual childish way.
Sylar went from hating Elle for her role in shaping him into the monster he's become to loving her to... hating her again and killing her. They have a very complicated relationship. In DDD, he still harbors a lot of bitterness towards her because of the circumstances that lead to her death. While he's not actively trying to make her life miserable, he knows she'll get hers farther along her time line and that thought is satisfying enough for him.
Sylar hates Peter. He hates Peter for his power, he hates Peter for being successful at life in so many areas where he fails, he hates Peter because Peter is the hero, he's the villain, and that's just plain how it's supposed to be. He was willing to play nice and try to understand when he thought they were brothers, but those times are over now. In DDD... very little has changed.
Rei mystifies Sylar. There's so much she flat out doesn't understand about being human, and he finds that fascinating. She always calls him out on it when he's being irrational, and to a degree he actually does appreciate that. And he really enjoys their philosophical debates.
In laymen's terms, Sylar thinks Azula is a spoiled, stupid bitch. She was his pet project in psychoanalysis for awhile, but those days are pretty much gone. He thinks she's a horrible person like he is, and will sometimes go out of his way to point this out to her.
Emo is the first friend Sylar made on the community, and their friendship is based mainly on talking shit. They've both had hard lives, so Sylar feels like Emo can relate to him to a degree. But ever since Jim left and Sylar's life basically came crashing down around him, he's done a swell job of pushing other people away. Emo included. :(
When Sylar first met Giselle, he pretty much... thought she was crazy. And too naive to exist. After a virus made them think they'd been living together (not like that) for some time, he's placed her in a sort of little sister role. He's protective of her ~innocence~ and sometimes shies away from her because part of that being protective means... protecting her from knowing the kind of person he really is.
Sylar hates Sulu. He hates Sulu a lot. This is based on when Jim was part of the community, and they had vastly different opinions of him and... him letting Sylar on the Enterprise for a few days. They had a phyiscal squabble. Now Sylar hates Sulu almost out of habit. And out of jealousy that he still gets to see Jim in some capacity while Sylar gets
a rock nothing.
Sylar basically thought Jim was a huge egotistical jackass, and related to him because he's also... a huge egotistical jackass. Jim actually listened to Sylar's problems and treated him like a person (because he didn't know any better) and Sylar appreciated that because he'd never had anyone like that in his life before. He'd also never had someone who called him out on his bullshit quite the way Jim did. After a virus made them think they were married for a week, they were left with a lot of forcibly-shoved-in memories and knowledge about each other that they never had before, and it brought them closer together. Jim basically made Sylar feel like he could be a better person during a time when he was attempting to reform. After Jim left the community, that all went to shit. Sylar took his leaving as a huge betrayal by the only person he'd ever trusted that much. It's still a sore spot.
Sylar relates to Shuyin. He thinks he understands him. Because they're both sociopathic all around horrible people. And Shuyin also has that whole living forever thing going for him. Which makes Sylar comfortable asking him advice about things of that nature and... well, life in general.
Sylar thinks Trish is really hot. He has a thing for blondes, okay. But yeah. She's attractive, confident, and all around a badass bitch. They often exchange flirty banter, but he's not interested in anything beyond that. Because he has 99 problems.