And HBP

They're all great, but I really liked the last two... But then there's The Prisoner of Azkaban... It's hard to pick! :)

Deathly Hallows
Order of the Phoenix
Prisoner of Azkaban
Goblet of Fire
Half Blood Prince
Philosopher's/Sorceror's Stone
Chamber of Secrets

i have two

Deathly Hallows
Half Blood Prince

It was hard between Chamber of Secrets and Deathly Hallows, but it's just....brilliant.

Favourites to leasts:

Deathly Hallows
Chamber of Secrets
Prisoner of Azkaban
Goblet of Fire
Half-blood Prince
Philosophers Stone
Order of the Phoenix

I though OFTP was very l-o-n-g and it took me ages to get through, I do really like it. But the other books -in my opinion- are just BETTER.

I loved all, and DH was truly amazing, but everyone loves it, I think, just because it was the end, and was very different than the others. My personal fave is HBP mostly because it deals with the past of Voldie and is very Draco heavy :) Here is my fangirlism, but apart from that, it is hard to say why, but it is my favourite.

maybe Deathly Hallows.

the last 3

Deathly Hallows
Prisoner of Azkaban
Order of the Phoenix
Sorcerer's Stone/ Philosopher's
Chamber of Secrets
Goblet of Fire