Best spreadsheet editor (tie): Quickoffice
Quickoffice's spreadsheet-editing module works very much like Excel, so it's instantly accessible to Excel users. That also means it offers less visual feedback than Apple's Numbers. Although it supports AirPrint and PDF export, it no longer supports editing from cloud storage services. However, it's the only app to support pane freezing.
Price: free with Google account
Developer: Google's Quickoffice division
Compatibility: iPad and iPhone