The best of a spotty lot, for me, is QuickOffice. I wish it had more features but for basic work it's okay, and its file handling and Dropbox integration are excellent. In fact, you can drag and drop files in Dropbox to organize them, which you can't do in the Dropbox app itself. The presentation tool works all right, too.
I need access to styles for some work so I use Pages for that. (Hint: get the 30-day free trial of Pages desktop to create your custom styles and export those templates to the iPad.) DropDAV works well, so I can access my Dropbox. Not being able to organize files within Pages is a real dealbreaker, though.
I tried DocsToGo but found it too buggy--selecting text was a nighmare, especially if I made it large enough to read easily.