If you can grab it, Microsoft Office 2004. To me, that's the last good release of Office. My choices, in descending order are:
1. Microsoft Office 2004
3. Jer's Novel Writer
2. AppleWorks 6 Yes I said AppleWorks.
4. iWork 08 (I think 09 required Intel, but I could be wrong)
5. LibreOffice
+1 for AppleWorks6. I did not mention it, because it will be hard to find these days. I often use it still. I like that you can choose to "save as" other formats. Also it runs quicker/ scrolls better, when one has pictures included or several pages (like in a scientific paper) in contrast to Word. I often use it to write the text first, then copy it to Word and just edit the styles.