Actually, I wouldn't say goodreader is a better PDF reader.. Using it through iBooks seems faster and snappier to me. The process is kind of a pain in the ass honestly. You basically have to get it to open through your mail or dropbox works too... Good luck! Might be easier getting it on goodreader however.
Goodreader works well, but you can add a PDF to your iBooks library, too.
Here's an article about how to get a PDF into iBooks using iTunes: How To Add ePub and PDF Books to iBooks on iPad
I hope this helps.