This is a no-brainer. PDF Viewer is built by the team behind PSPDFKit, the top mobile PDF framework incorporated into apps like Dropbox, Box, HipChat, Evernote and Ulysses and used internally by companies such as IBM, SAP, United Airlines, BMW, Audi and many more. In short, these folks really know the ins and outs of PDF.
PDF Viewer is free on the iOS App Store. Here’s the iTunes link. Go get it.
UPDATE: PDF Viewer was just added to the “New Apps We Love” list in the iOS App Store. Well that didn’t take long!