I have been running Office 97 since that version chugged to a halt with my second computer. It does everything I need, and is much cheaper than the newest version.
It also has the advantage of being thorouchly tested in the marketplace, and aside from that annoying paper clip thingy, does what I need without problems.
If you want the latest, with all the whistles and bells, it usually costs more.
I haven't checked out Open Office yet, but will get it for the next computer and 'play' with it.
That being said, Office 97-2000 was probably the best Office Suite. If Apple would fix a few things in iWork, it would be great, and only costs $79.