I had to put this one up, even though I'm only on the third one, I would say, probably the third one. Also, post why you like the book.

My Reason: I love the beginning

"I-WOULD-LIKE-TO-SPEAK-TO-HARRY"

I just love that.

I'm completely obsessed with them all, but probably the seventh one coz that's one they finally defeat Voldemort and there's heaps more epic stuff going on coz they're not at school (though Hogwarts is awesome).
Sorry for spoilers...

2nd one
it's the best of da movies, too. it has a GIANT SNAKE!!! also i first saw it in the cinema with my friend it was sooo cool

...but we also nearly shat ourselves when the basilisk appeared