This is the key question. If you're going to be writing for yourself, Pages will probably do the job. If you're going to deal with people who only use Word and you need perfect compatibility, Office is truly the only way to go (what's more compatible than the same product?). How do you plan sharing documents (if at all) and with whom?

As an aside, this is where I really wish MS sold the Office products separately like they do for the Windows version.