A question for the Mac users out there

What word processing program do you use, and do you like/dislike it? I am about to embark on a writing project of some substance, and the free program I am currently using is not working so well for me.

People either seem to love or hate IWork, and love or hate Microsoft. And I can't for the life of me figure out if one is better than the other, or if they both suck.