When comparing Little Snitch vs RCDefaultApp, the Slant community recommends Little Snitch for most people. In the question“What are the best Mac OSX apps for someone that's new to Apple?” Little Snitch is ranked 7th while RCDefaultApp is ranked 24th. The most important reason people chose Little Snitch is:
Little Snitch rules work even at login screen. Even when receiving attempted connection alerts, once logged in LS has stopped and requested permission for them.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Protected even at login screen
Little Snitch rules work even at login screen. Even when receiving attempted connection alerts, once logged in LS has stopped and requested permission for them.
Pro Comparatively easy to use
Easier to use than traditional firewall software, but more powerful due to design and workflow.
Pro Protects your privacy
Protects your privacy and helps to prevent unwanted connections.
Pro Provides missing functionality
Standard features on Windows, but not on Mac, this fixes that.
Cons
Con Last update was in 2009
But the software still works, so far no issues on El Capitan 10.11.3.