I am mostly a user of Excel files, and also struggled with which app to use. After some pocking around the web, I chose an app based on functionality for its app cost, and chose QuickOffice Connect HD. What made this one my choice was that it was $10 and I could easily move files from my pc to the iPad using a http address that they display to you in the app, as long as you are on the same wifi network (ie not internet, just local wifi) or using a document or file repository like GoogleDocs. But as I used it I found that it lacked in the ability to use large Excel files 2mb was one that I tested. I had to downsize my xls file to use it in this app. Also Freeze Panes, something that I use all the time was not available and simple functions were hard to use in their interface.
Quickoffice Connect do offer on their support website a feature request submission with ratings which allows use to suggest what you think should be added, but they don't upgrade their versions fast enough for you to take advantage of them. I personally think that that is because each new version on the app store causes an erase of their app ratings (current version) and so they may want to release slower to allow more reviews. That's just my opinion.
I may buy Docs2go hd because they have an app on the Blackberry too and they have freeze panes and the way they approach menu items is a bit nicer. Overall, I think neither of them are perfect. Would be awesome for Microsoft to offer it on the app store!
