Document fidelity with these apps has greatly improved over the years, but still isn't perfect. On one of my test Excel spreadsheets, Quickoffice did not adjust column width to accommodate a lengthier entry, while Docs to Go did. In general, Quickoffice has the better-looking interface--it shows tabs on Excel workbooks with multiple spreadsheets, and its file management system is intuitive and color-coded (Quickword docs in blue, Quicksheet in green, and Quickpoint--the PowerPoint competitor--in orange). Docs to Go puts its file locations and tools at the bottom of the screen in gray.
But neither app was able to open a complex Excel file involving macros that transfer data to multiple sheets.
As for document portability, both Docs to Go and Quickoffice provide good integration with popular online file storage and management services. Both let you access and save files to Google, Dropbox, Box.net, and SugarSync; Docs to Go additionally supports iDisk, while Quickoffice has support for Evernote, Catch, Huddle, Egnyte and MobileMe. You create these connections in the settings, and thereafter they are easily accessible.
Office 365 Web apps automatically save documents to SkyDrive, as do Office desktop apps that are part of an Office 365 subscription.
Getting files to your desktop isn't quite as straightforward with mobile productivity suites. Docs to Go provides a desktop app that lets you sync the contents of any folders you choose with the mobile app. This works well as long as you don't choose a huge folder to synchronize; by default, Docs to Go sets up an empty My DocsToGo file for this purpose.
Quickoffice has no comparable means of saving to a desktop, but it does offer workarounds. When your mobile device is on the same Wi-Fi network, you can access and upload files using a desktop browser by typing in the URL shown in the app's home screen. You can also mount the device as a network drive (using the same URL). With iOS devices, you can use iTunes to synchronize files.