Multiple methods of parsing JSON data are available to iOS developers, but it is not clear which of these libraries is the best option. We investigated this problem by benchmarking the performance of several JSON libraries for iOS:
YAJL
Touch JSON
SBJson (previously json-framework)
the native JSON parsing library (only available in iOS 5.0+)
Read More - http://tech.xtremelabs.com/ios-json-parser-comparison/