QuickOffice HD might be the best of the lot, but all office suite programs on phones/tablets have some issues with the proper display of complex documents and files. Docs to Go isn't bad, either, based on my past experiences with it on various mobile platforms. None of these is really useful for complex editing of documents, spreadsheets, or presentations. For simple stuff, it works pretty well. It's nicer with the BT keyboard and mouse.
Cheers.