iH8Sn0w says there is a possibility an untethered jailbreak will be released for iOS 6.1.3/6.1.4 and recommends staying on iOS 6 or downgrading back to iOS 6 if you are already on iOS 7.
Apple has officially released iOS 9 for public download with new multitasking features for iPad, transit directions in Maps, a redesigned Notes app, a new News app, and Siri improvements.