As previous posters have pointed out, it depends on what you are doing.
Word tends to crash on me at bad times, on all three of my machines. It also likes to 'get in the way', it thinks it knows what you want to do and most of the time it's wrong. That being said it does have nice features, a programmable autocomplete, grammar checking, etc. Word is also a necessary evil, nearly every time I collaborate with a peecee user, all they know/have is Word.
Pages excells at layout, formatting, and document presentation. Real time text wrapping and object alignment guides are amazing. Pages' handling of paragraph styles is far superior to Word's.
Both programs tend to get bogged down with large documents and embedded pictures (1.33 PB, 768 Mb). For instance when scolling a ten page lab report with figures (not really all that large a document even), Word just shows lots of blank space for the figures and takes a while to display them once you've stopped scrolling. Pages on the other hand will show you everything in the document as you scoll by, but will move like molasses.
Pages is not ready ( and possibly not yet intended) to replace Word. Give it two more versions and we'll see. I've switched to writing my documents in TextEdit (lightweight and fast) without any formatting other than paragraph breaks, then doing the layout in Pages.
Last thing, I recently downloaded a trial version of
Mellel and it looks like it could be a contender to become my primary word processor.