I've tried NeoOffice, OpenOffice, iWork, and Office 2004 on my Mac. I personally don't like how OpenOffice looks, though that problem is solved with NeoOffice. The only problem with these two is that they seem to take a while to load and once they do, they don't seem to be very polished.
Office 2004 works just as well as its Windows counterpart. I have the same issue as with the other two suites, it takes a while to load. However, this one is much more polished and is easier to use because I'm so used to Office. Plus, the Student version makes it very affordable. I will definitely be upgrading to Office 2008 when it comes out because it should load faster since it will run natively rather than under Rosetta.
Finally, iWork. This is the program I use 90% of the time. I use it to take notes in class and to write my papers. It loads very quickly and is a piece of cake to work with.
The only time I use Office is when I need to look at Word documents with lots of formatting or if I need to use Excel since iWork doesn't come with a spreadsheet program...yet.
Since you're switching soon, I would suggest checking out NeoOffice, Office 2004, and iWork. The last two come with trial versions on all new Macs (don't be put off by the word trial, they're fully functional and the trial lasts for a pretty long time).