The werewolves don't like the Cullens because as werewolves/shapeshifters, they have an intrinsic animosity towards all vampires. They smell vampiric venom and instantly think "enemy". Even though the Cullens don't hunt humans, the werewolves think of them sort of like a ticking time bomb. The werewolves who don't like being werewolves also blame the Cullens' presence for triggering their phasing and the negative effect that's had on their lives.
The Cullens mainly dislike the werewolves because they're picking up on this animosity and reciprocating it. They also feel that the werewolves smell weird - kind of like a wet dog smell - and they worry about werewolves being a danger to Bella because of how they can't always control their phasing when they're new to being a werewolf.
