Apple's Pages is good at layout-oriented documents, and it offers revisions tracking, tables, spell checking, search and replace, text formatting, graphics insertion, commenting, password protection, AirPrint support, and both ePub and PDF export. It also permits multiuser editing via the Web (but with no revisions), now with password protection.
The mid-October update added direct access for saving and opening files from both Apple's iCloud Drive and third-party cloud storage services (Box, so far). Pages also supports Apple's Handoff capability for Pages on other iOS devices and Macs.
You must copy a file before editing, as there's no Save As feature once you begin editing. You can't create or apply character styles, and you can't create paragraph styles.
Price: $9.99 (free on new devices)
Compatibility: iPad and iPhone