For more recent devices, your best option is to get to the 5Ghz spectrum, especially if all of your equipment can support 802.11ac or newer. But for the question as it relates to the 2.4Ghz band:
Stick to 1, 6, or 11!
And for best results, get your neighbors to do the same.
Even if other channels seem less crowded, remember that because channels overlap you still have to deal with interference from those busier channels as well. Your "clearer" channels will still have interference originating from the busy channels, so there is little to gain. What happens when you put your system in between two of the "standard" channels is that now you get interference from both of them. So, if you were to use, say, channel 3, you might now get interference from radios on both channel 1 and radios on channel 6 (and everything in between). More than that, you will yourself now cause interference with people using both of those channels. Whenever that happens, those other users will have to re-transmit their message, making the wireless signal in your area even busier.
There are a few studies indicating that, under the right circumstances, it may be possible to get more throughput using a four-channel scheme (such as 1,4,7,11, 1,4,8,11, or 1,5,8,11). However, for this work everyone in your area would have to agree on it. Until you can get everyone cooperating on that scheme, you will get best results by using the least busy of 1,6, or 11. Even then, this was only shown to help for certain kinds of loads and densities.
Finally, be careful when deciding which of 1,6, or 11 is least busy. Tools like InSSIDer will not help you here. They will only show you which neighbors have the strongest signal available on which channels, based on beacons from the access points/routers. They will not tell you how much those neighbors are using the signal. If you have someone next door with a strong access point on channel six, but they hardly ever use it, and other neighbors down the way with weak access points on channels one and eleven, but they use them to work from home and are on them all the time, you may be better off using channel six, even though it might look "bigger" in a tool like InSSIDer.
So how can you know which channel is least busy? This article on the serverfault blog may help:
http://blog.serverfault.com/2012/01/05/a-studied-approach-at-wifi-part-2/
It's the 2nd part of two part series, but the first part is less important to this discussion. The main thing is they recommend a tool called Vistumbler that will allow you see not just signal strength, but also actual traffic. It's takes a bit of doing, but you can use this to really know, not just guess, what channel is typically least busy in your area.
1
A lot of people mistake IEEE 802.11 signals for solid cars on a multi-lane highway. They frown upon people driving over the lines, occupying more than one lane. However, Wifi signals are rather like colored plumes of smoke. Along the open lanes, the color plumes are allowed to intermingle. As long as I can still tell the color of my plume of smoke at the end of the road, all is fine. The partial overlap of differently colored plumes is then like a gray mist of noise to my signal. This is the principle of spread spectrum communication. More info here.
– Serge Stroobandt – 2014-07-06T15:08:29.71713"the only non-overlapping channels ... are 1, 6, and 11." - You misunderstand the concept of "non-overlapping channels". There are groups of non-overlapping channels. 1, 6 and 11 is only one of those groups. If your neighbor is using channel 5, then if you try to use ch 1 or 6, then you will overlap with his signal. – sawdust – 2012-06-29T21:24:00.447
4@sawdust I understand that just fine. Let me amend that statement then - the largest number of non-overlapping channels are the 3 channels 1, 6, and 11. I'm saying that since EVERYBODY uses 1, 6, or 11, should I still use 1, 6, or 11? Or is it better to use 3, 4, 8, or 9 which are in between these popular channels. – Luke – 2012-06-29T21:40:07.470
3Probably the best way to find out is to ignore all this conflicting advice, setup iperf on two machines, and test the throughput of each channel. – endolith – 2012-12-14T17:18:37.270