Right now, I don't see a good reason for the IBM offering (apart for, if you are an existing IBM customer you can probably get all your support from one place). I'm expecting it to show substantial progress over forthcoming releases, so this may well change. And if OO were not available, you'd probably use Symphony quite happily, but right now, I can't see any good reason for most of us to prefer Symphony over OO.
The comparison between koffice and OO is a bit different; the koffice word processor behaves more like a cut-down DTP program than a traditional word processor (and looks a bit plain, imho - but then I have seen some builds of OO look very plain, too). So, if you choose which of those ways of working you prefer, you should be there.