Long story short? SAX is faster. There, you don’t have to read the article.
Since it’s no secret that fetching Issues from Launchpad, Google Code and Bugzilla involves parsing RSS/ATOM feeds, I decided to poke around and investigate which parser to use and the advantages each carried.
After a few seconds of Googling, I found this article, over at Developer.com. Their math seems solid. I’m sticking to SAX.
Abugadro