To determine which channel you should use, you need to consider your wireless environment and the devices you use
One of the first things you should research while determining the channels you should set your access points to is which channels your devices support. Some devices will not support certain channels, so if you have an access point set to those channels, you will not be able to connect to the network. An easy way to find this information is going to https://clients.mikealbano.com/. This website is a large list of devices and their capabilities.
Spectrum Graph (Wireless Environment)
This graph will show you all of the access points within range of your device and the channels they are using. The importance of the spectrum graph is that you can see which channels are congested and which channels are open.
As you can see from this spectrum graph, a lot of channels are being used by many different networks.
Choosing a Channel
After determining which channels your devices are capable of using, and looking at your spectrum graph you have a much better idea of which channel to choose.
If there is an open channel that your devices can use. Then, that is probably the best channel to assign to your access point.
If there are no open channels, find a channel that has the least congestion and the lowest signal to your device. The stronger the signal is, the more likely you will experience interference.