Wireless environments are unique and can vary over short distances and time periods. So there is no universal best channel, the best channel will depend on your unique wireless environment at the time.
The 2.4Ghz band is narrow (83.5Mz wide), made up of 13 overlapping 20Mhz wide channels. So, there are practically only 3 non overlapping channels that do not interfere with each other, disrupting your wireless signal.
The autochannel feature is as effective as it's algorithm, as there is no standard how the software should be impletmented, it was developed just to appease the WiFi Alliance toi allow channel bonding on the 2.4Ghz band. So, many autochannel algorithms will just scan the local environment and pick the less congested "primary" non overlapping channel (1,6,11) ignoring overlapping channels which will cause more disruption than networks on the same channel.
I would download a wireless scanner like InSSIDer or WiFi Analyser for Android to help you manually choose the best channel. Bear in mind the wireless scanner will not pick up interference from domestic devices like A\V Streaming devices, Baby monitors, Chordless phones, Microwave ovens, Plasma TVs. Security systems etc,