Best presentation editor: Apple Keynote
Simply put, iWork Keynote is an amazing slideshow editor. We 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, plus the ability to remotely control a Keynote presentation on another 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.