Out of all the characters, who knows how to throw the best disses?

For me, I think Harry. Especially in the order of the phoenix.

I think Draco has quite a few snappy comebacks. My personal favorite is from "Prisoner of Azkaban" when he responds to Professor Lupin with "This class is ridiculous."

I think it's Snape

Hermione for sure. My favorite is about Pansy Parkinson in HP5- "how she got to be prefect when she's thicker than a concussed troll..."

I think Harry, Harry is so snarky, sarcastic, and sassy and I love It.

Uncle Vernon: What were you doing under our window, boy?
Harry: Listening to the news.
Uncle Vernon: Listening to the news! Again?
Harry: Well, it changes every day, you see.- Order Of the Phoenix

Malfoy: 'You're dead, Potter.'
Harry: Funny, you'd think I'd have stopped walking around:'
Malfoy:'You're going to pay,I'm going to make you pay for what you've done to my father:'
Harry: 'Well, I'm terrified now,I's'pose Lord Voldemort's just a warm-up act compared to you three - what's the matter? He's a mate of your dad, isn't he? Not scared of him, are you?'
Malfoy: 'You think you're such a big man, Potter,You wait. I'll have you. You can't land my father in prison - '
Harry: 'I thought I just had,'- Order Of the Phoenix

Dudley: They stuff people’s heads down the toilet the first day at Stonewall. Want to come upstairs and practice?
Harry: No, thanks. The toilet's never had anything as horrible as your head down it—it might be sick.- Philosopher's Stone

Snape: Do you remember me telling you we are practicing nonverbal spells, Potter?
Harry: Yes.
Snape: Yes, sir.
Harry: There's no need to call me "sir," professor.-Half Blood Prince