I wish I had read the whole trilogy before seeing the movie, but what's done is done.
I tried to read FotR when I was about 12 and the pacing was just too slow-- I got bored and didn't pick it up. Then I saw the movies of FotR and TTT, and thought they were amazing. I didn't have the strength of will to wait another year to find out what happened, so I went and read the whole trilogy.
And thus an obsession and a sudden pasty quality to my skin from sitting around doing dorky LotR-related things (ie: learning Quenya) were born.
Not that there's anything wrong with that sort of thing
But, yeah, book before movie is always better.