So I understand that there are a few options available as far as parsing straight XML goes: NSXMLParser, TouchXML from TouchCode, etc. That's all fine, and seems to work fine for me.
The real problem here is that there are dozens of small variations in RSS feeds (and Atom feeds too), so supporting all possible permutations of feeds available out on the Internet gets very difficult to manage. I searched around for a library that would handle all of these low-level details for me, but came out without anything.
Since one could link to an external C/C++ library in Objective-C, I was wondering if there is a library out there that would be best suited for this task? Someone must have already created something like this, it's just difficult to find the "right" option from the thousands of results in Google.
Anyway, what's the best way to parse RSS/Atom feeds in an iPhone application?
"Best" is relative. The best performance you'll need to go the SAX route and implement the handlers. I don't know of anything out there open source available (start a google code project and release it for the rest of us to use!)
Whatever you do, it's probably a really bad idea to try and load the whole XML file into memory and act on it like a DOM. Chances are you'll get feeds that are much larger than you can handle on the device leading to frequent memory warnings and crashes.