A new office productivity suite -- Office2HD -- has unseated our previous co-winner, Quickoffice Pro HD, in the word processing category. Office2HD offers the editing and formatting you'd expect, including support for multiple columns and images. But it does more than the rest: It lets you add comments, footnotes, endnotes, column breaks, and section breaks, plus -- the big deal -- track changes made within Office2HD.
Although it can't apply paragraph and character styles to text, Office2HD preserves those already in your documents. Also, you can search but not replace, nor apply or edit embedded hyperlinks. Office2HD supports a wide range of cloud services, but not iCloud.
Developer: Byte Squared
Compatibility: iPad (iPhone version sold separately, $5.99)