After some research a while back, I prefer and have been using Repligo. There's no subscription and it's on device (files don't go back and forth to someone else's server).
When I bought it Docs to Go didn't have PDF reader available, but even after, I like the idea of a focused company. They've been exceptional replying to emails, etc.
Check... RepliGo Reader for BlackBerry - Native PDF Viewing
Free Trial, so check it out.
Purchase price shows as $19.95