The Best Office on iOS

• Documents: supports major cloud disk. Good viewer in general. But compatibility with MS Office formats (especially docx and pptx) is as bad as the native iOS viewer.
• QuickOffice (free): only supports Google Drive (of course...after being acquired by Google). Very slow on iPad mini. The compatibility with MS Office is good but formatting is not accurate.
• CloudOn (free): supports major cloud disk. Although on the cloud, it is as fast as, if not faster than, native software. Exact formatting like you see on PC. 100% compatible!
• Office 365: no money to try...