The Book surely. Personally I don't think there's a debate about that. :)

Somehow, harry potter movies fail to impress, partly may be , a single film cannot accomodate complete book, and partly , may be , they have less time as actors are getting older and may not fit into the charactes after some yrs, hence producers r in hurry to complete the series.

the book is better the movie made me feel sleepy, and i went to watch dis movie wid my mates so i found it more intresting to annoy dem =/

The book was way better than the movie .Movies generally arent as good as the book because they are not able to incorporate all the details that the book has but this movie failed on other accounts. This movie was supposed to give a detailed account of the history of Voldermort , he is a very important character and I think his history deserves more mention than the romance between the characters.
The climax scene in which there is a fight sequence between the Death Eaters and the members of the Dumbledore's Army was worth a mention too...instead we just see the destruction of the Hogwarts Hall by Bellatrix.
The burrow was burned down for no reason at all...and there were many characters from the book which were missing in the movie...
The movie was very slow and was not able to capture the audience's interest. The only scene which stood out in the whole movie was when Dumbledore and Harry go to find the horcrux in the cave by the sea.
In short David Yates misses all the main points which the movie should have shown. This movie was the most awaited and the most disappointing of the lot.

The book was better than the movie..
The movie did good, but it missed many important parts of the story.The movie forgot the main part of "The Half Blood Prince" that was to highlight on the spells and the nature of Snape. There was just a dialogue "Do you think you can use my own spells against me?".Morever, there was no vivid description of Voldemort's dark past. I am not trying to say the movie was totally bad or waste of money but it missed soem of the most intrestng parts..

First thing first, i watched the movie yesterday and i liked it. Script is well written though a lot of important incidents from the book were missing. But i would stand on my view that book was far better than the movie as it gives you more detail and keeps you bind with it, while the movie was lacking it. Movie gave very less importance to voldemort's past which was the highlight of the book. Also too much importance was given to the love angle in the movie, because of that it felt quite slow at times.