I have both OO and MS, but am mixed. I dread the fact that you need to run X11 to get OO to work (Why can't they rewrite the program for MacOS X now that the Mac is such a popular platform?). Because of that, it takes forever to load the program when you try to launch it, and I always get an error message that I have to click OK to before it is ready to use.
However, once running, OO is better. MS for Mac doesnt have Access, so this negates any benefits it could have over OO anyhow. Meanwhile, OO has EXPORT TO PDF, which I use more often than either ODT or DOC file formats.
So, I prefer Open Office, but I hate X11.