I really don't think it is fair to compare them. LOTR is a thoroughly researched peice of fiction, which was written over a number of years, has a comprehensive backstory, languages that you can actually use and was a groundbreaking peice of work.
Harry Potter is an entertaining story that (from what I can tell, and I will wait until my kids are old enough to be interested in them and read the books with them, cos they are kids books) has stolen lots of different ideas from previous works or fiction and mixed them all up into a very enjoyable read. However, it's popularity and commercialisation has kinda taken the edge of it for me. HEnce why I will wait and read them with my kids.
LOTR I can read again and again.
And with the films, the extended versions are the best. And I also don't think you can compare Return of the King, which won the most Oscars ever (ok along with a couple of others- Ben Hur and Titanic) with the Harry Potters, however popular they are.
Now Terry Pratchett, that is a whole other fantasy world, and he even wrote books with Cameras in them.....................