I’ll vouch for NeoOffice/J. It launches will all the nimble alacrity of the Queen Mary II pulling out of port, but it’s more compatible for opening Word documents than anything else I’ve tried. (And it’s not slow to use, just to launch). The combination of excellent compatibility and free price make it a clear winner.
AbiWord. Requires the X11 environment. Also free. Smaller than NeoOffice/J, launches faster. Less compatible, doesn’t handle all Word documents. Note that printing from an X11 application can be an exercise in Unix-think that you may or may not find appealing.
OpenOffice. Requires the X11 environment. Also free. Looks and feels more like Word than AbiWord but no more so than NeoOffice/J. Not small. Same problems as AbiWord w/regards to X11ish considerations.
AppleWorks, iWork. I’ve never used iWork so I’ll just assume that most of the same applies. Not free, although some Macs come with it preinstalled. Cheaper than Word (substantially so). Less compatible with Word than the rest, in my experience. Word processor module doesn’t look or behave at all like Word, which is either wonderful and nice (if, like me, you really really hate Word) or far from wonderful and nice (if you want the look and feel of Word when you’re composing/editing/viewing documents). NeoOffice/J and OpenOffice are far more Word-like.
MacLink Plus. This is not a word processor (or office suite) at all, it’s a Swiss-Army knife of translators. If you wish to view your Uncle Tommy’s Word documents in Nisus or MacWrite Pro or WriteNow, or you need to convert your own AppleWorks WP documents for your Mom who uses Lotus WordPro on her PC, this is the tool for the job. (It also does spreadsheets, which can be useful. And graphics files, which is redundant if you have GraphicConverter). Not free. Not as compatible with Word documents as NeoOffice/J but more versatile and lets you use the word processor of your choice.
Word itself. Word X has its fans. If you actually like Word, the OS X version is actually regarded as better than the Windows version by many people. As you’d expect, it’s extremely compatible. (It won’t do object linking and embedding but neither will any other Mac solution. That technology just never landed on our side of the river. Chunks of spreadsheets linked from Excel documents aren’t going to make it in your Word documents on the Mac, unless Microsoft did something in very recent history that I don’t know about). Word X may even be too compatible with Word for Windows, as it will execute Word macros including macros that are effectively viruses and will insert themselves in all other Word documents. Word macros don’t do any damage on a Mac but they can spread to other Word documents that later get on PCs and mess them up. Oh, and Word is expensive. If your’e a student you can acquire it more cheaply. You can also often score a copy on eBay, although I can’t promise the legitimacy thereof.