Most annoying character?

Georgina Sparks actually gets things done and is probably one of the smartest and most talented people in Gossip Girl .

Ivy is beyond terrible and should have been thrown in federal prison. Her mother Carol should have also been thrown in federal prison.

Outside of Vanessa Abrams's massive hypocrisy and hers trying to sabotage others for personal gain, much of Dan Humphrey's careers is because of her deciding to get his work published.

Without Serena Van Der Woodsen, her brother probably would have killed himself, Blair Waldorf would have been miserable her entire life, Dan may have been a nobody his whole life, etc. She's ultimately a positive for the world.

Chuck Bass eventually becomes at least somewhat of a good person and certainly becomes the most mature and 'wisdom-giving' of the main characters.

Much of Lily's life has been miserable simply because her mother Cece didn't want Lily remaining with Rufus.

Without Carol, Lily obviously would likely have never met Rufus.

Overall, Ivy is the worst.

The latent causes of faction are thus sown in the nature of man [...] views

I agree about Sage; she was awful in every way!