Best presentation editor: Keynote
Simply put, iWork Keynote is an amazing slideshow editor. I prefer it over PowerPoint even on the Mac, and on the iPad it works beautifully when creating complex slide transitions and element effects, which competing apps can't do. The newest version adds more animation capabilities and (unsecured) Web-based collaborative editing. A bonus is Apple's free Keynote Remote app that lets you remotely control a Keynote presentation on your Mac, iPad, or iPhone.
Keynote's big negative is its awkward requirement of copying documents to and from cloud storage services, rather than allowing direct access. But it supports AirPrint and PDF export.
(free on new devices)
Compatibility: iPad and iPhone