For more recent devices, your best option is to get to the 5 Ghz spectrum, especially if all of your equipment can support 802.11ac or newer. Soon, we will also have 6 Ghz spectrum to play with.
But for the question as it relates to the 2.4 Ghz band:
Stick to 1, 6, or 11!
The thing to understand is the channels are only 5 Mhz wide. Channel 1, for example, centers at 2412 Mhz, and Channel 2 centers at 2417 Mhz... only 5 Mhz later. But wifi uses at least 20 Mhz of spectrum. So a wifi radio using 20 Mhz centered on Channel 1 will have signal going up to 2422 Mhz, well into Channel 3. A wifi radio centered on Channel 6 (2437 Mhz) will range down to 2426 Mhz, below Channel 4, and as high as 2448 Mhz, past Channel 8.
And that assumes only 20 Mhz channel sizes. 40 Mhz is also common in the 2.4 Ghz range. If you're using 40 Mhz channels (or greater), things are limited even more.
Best results come when your wifi signals do not overlap, and using only 1, 6, 11 with 20 Mhz channels gives the maximum potential. This is especially true in high-density areas, such as large apartment buildings, so for best results get your neighbors to do the same. Note that 20 Mhz channel widths will reduce the maximum theoretical speed, but it makes it more likely to have consistent reliable throughput, especially if your neighbors are on board.
Of course, if you live by yourself in the middle of nowhere, feel free to run a single radio using 80 Mhz signaling on whatever channel you want.
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:
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.