Let's face it, the office suite options on Ubuntu aren't as good as they should be. (I'm going to talk mostly about word processing here.)
OpenOffice.org has most of the features anyone needs, but it is big -- really big -- and slow. It's leaps ahead of Star Office 5.0, OO.o's predecessor when I used it years ago, but OO.o moves forward relatively slowly and is notorious for having very little community contribution. Most of the new code comes from inside Sun. It uses the ISO standard ODF file format by default.
Gnome Office has some good, fast applications, but they aren't well integrated, and it doesn't sport anything for presentations. The word processor, especially needs more features to be a competitor, but that isn't likely to happen because Abiword prides itself on being small and agile with fewer features.