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.

The proof of the pudding is in the eating!

1-6-11 is often worse in moderately congested areas

The 1-6-11 recommendation contained in Cisco's whitepaper about IEEE 802.11 deployment in the corporate environment certainly does not apply to all circumstances, especially in non-corporate settings! For example, in moderately congested neighbourhoods, one stands a very good chance to benefit from not sticking to this proposed scheme. So, don't be a monkey and consider this:

• First, note that the signal of a device on a partially overlapping channel is merely noise to the device on the overlapped channel. This is entirely intentional by design. The technique employed by 802.11b is called spread spectrum, or rather direct-sequence spread spectrum (DSSS) to be precise. 802.11g circumvents in-channel noise through orthogonal frequency-division multiplexing (OFDM) of a multitude of narrow (hence slow but more reliable) carriers.


• However, the situation usually gets worse when one voluntary abides to the 1-6-11 non-overlapping channel scheme. Doing so will expose your devices to the IEEE 802.11 RTS/CTS/ACK (Request to Send / Clear to Send / Acknowledge) of alien devices, effectively silencing your devices and hence forcedly lowering your bandwidth. This problem is known as the exposed node problem. In a corporate setting this problem can be solved by synchronising the nodes. In the wild, this is not readily achievable.


• In the end, Shannon's theorem is what dictates the maximum achievable information transfer rate of a channel in function of the noise level on that channel.


• Your antenna might provide more gain on certain channels and/or in certain directions, both greatly affecting your signal-to-noise ratio.

Hence, I call for actually measuring one's own signal-to-noise level. On a busy time of the day, try a number of seemingly quiet channels in between the most busy channels and far away from the strongest alien signals.

On a GNU/Linux system you can list all access points seen by your WLAN device as follows:

sudo iwlist wlan0 scan

Your own network will also be listed with a Quality value, roughly proportional to the signal-to-noise ratio. Try to maximise this value by changing channels and/or improving your base station antenna gain in your direction (e.g. by using a sector antenna at the edge of your home). Note that antennas often provide a little bit less gain at the band edges (channels 1 & 13/14). Maximum Quality is what you are looking for. The Quality value takes into account noise from overlapping channels.

Channel:3

Frequency:2.422 GHz (Channel 3)

Quality=70/70  Signal level=-40 dBm

If 2.4GHz is too crowded, you may consider falling back to RTS/CTS/ACK channel sharing in the 1-6-11 scheme. Still better; do yourself a favour and upgrade your devices to 5GHz. Much more bandwidth is available on 5GHz and overlapping does not exist.

The important lesson here is: bandwidth is a finite resource. It is especially scarce on the lower frequency bands (2.4GHz).
Like with any scarce resource in life, there are only a limited number of possible approaches, listed here using metaphors:

• The 1-6-11 non-overlapping channel scheme would be the equivalent of a state-sanctioned communist planned economy (i.e. all too often like internal corporate culture).


• Signal-to-noise optimisation is blatant libertarianism and probably more efficient.


• And migrating to 5GHz should than be something like... colonising Mars.

In big corporate networks it's common practice to use channels 1,6 & 11 because it is fairly straightforward (at least on a diagram) to design non-overlapping cells of coverage. As a home user you don't have the same constraints so it makes sense to experiment and look for the best channel. inSSIDer is free and quite popular for checking what's going on in your neighborhood. Collisions will only occur if the interfering signal is strong enough to interfere with the wanted signal. So if your laptop was right next to your AP pretty much nothing is going to interfere. That's generally not the case so it's normally a case of trial and error (and monitoring) to determine the best channel. Plus if you have a few people in the same area all constantly checking for the best channel it can get a bit messy.

Well, I am a Ham Radio operator. I have done extensive testing. On my Actiontec or ZyXcel, channel 1 is abysmal! Channel 11 is a close second to the death of channel 1. ACTUAL power readings put 3 and 4 as the strongest signal output and throughput. Channels 6 and 9 are the standard preset. so actually avoid 1,6,9,11. I am a DSL tech also. I have walked people through changing channels from 9-10-11 to 3 or 4. They are amazed at the doubling of the wifi signal on all devices across the board. Leave the signal strength analysis to the experts kids. (it has to do with the relationship of the stage 1 pre-amp I F and the final stage RF, and just never mind)
;o)

In practice there doesn't seem to be too much difference, but if a channel is way overcrowded (e.g. with more than 4 APs using it), you might want to consider switching to a different channel to reduce the likelihood of the signals getting mixed up or otherwise interfered with by other signals. It also sort of depends on your signal strength. If your signal is really strong, it doesn't matter.

Some great answers here, but others that just don't understand the technology.

Let me answer with a fictitious, non-technical example. Let's imagine a world where the "highways" are 11 "lanes" wide and the vehicles are 5 lanes wide. Driving part way on the "shoulder" is allowed.

If there is a vehicle going slowly centered on lane 3, this would cause congestion for vehicles centered on lanes 1 and 6. Conversely, if there was a fast vehicle centered on lane 3, it would be impeded by a slow vehicle centered on either lanes 1 or 6.

The best way for traffic to flow effectively and efficiently is if the vehicles are all centered on lanes 1, 6 and 11.