What wireless channel to use in a crowded space
And again for the best throughput and minimal interference, channels 1, 6, and 11 are your choice. Depending on the neighboring WiFi networks one channel can be a better choice than another.
E.g. if you choose channel 1, but your neighbor is using channel 2, then you'll want to switch to 11 to completely avoid overlapping, though 6 can work as well if not better. As tempting as it is to use the channels other than 1, 6, and 11, remember that everyone around will be stomping on your throughput and you can become the reason for channel interference.
It would be a perfect setting to talk with all the neighbors and set up each router to channels 1, 6, 11. If you have a thick brick wall between you and your neighbor using the same channel 1 probably wouldn't hurt, but if there is a thin wall between you, try working on using different wireless channels.
5 GHz channel band
The 5 GHz (802.11n and 802.11ac) band actually offers way more free space at the higher frequencies. It offers 23 non-overlapping 20MHz channels.
Starting with 802.11n and going to 802.11ac, wireless technology became much more advanced. If you bought a router within the last couple of years, then you probably have a decent 802.11n or 802.11ac router. Most of them have a hardware inside that automatically selects the proper WiFi channel and adjusts the output power thus boosting throughput and cutting down the interference.
Using the 5GHz band and having decently thick walls as well as the general lacking of 5GHz devices usually means that there is a very little interference in your space. In cases like this you may benefit from using the 40, 80, and 160MHz channels.
Ideally, as everyone gradually upgrades their hardware and starts using 5GHz band, having to select the proper WiFi channel will become obsolete. It is especially applicable to MIMO setups (up to eight in 802.11ac), when it is a better idea to let your router do its own thing. Of course there will be custom cases like fine-tuning the channel selection for your router. Eventually, even the 5GHz will fill up, but by the time it happens we should be able to figure higher WiFi channel frequencies out. Or maybe entirely new antenna designs will be created for the high-end demands of wireless networking world.