There may be more routers using the 2.4 GHz band in your area than using the 5 GHz band, so finding a relatively empty channel with little interference is much easier. The 5 GHz band also often has more bandwidth, so you might see higher transfer speeds on that band.
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Intermittent problems are often a result of interference. Interference can be caused by other wifi networks in the neighborhood or from many household electrical items.
You can download and install iStumbler (NetStumbler for windows users) to help you see which channels are used by neighboring networks so that you can avoid them, but iStumbler will not see household items that cause interference.
Refer to your router manual for instructions on changing your wifi channel or adjusting your multicast rate (which may help where interference is present. You might also try moving the Apple TV away from other electrical equipment.
There are other types of problems that can affect networks, but this is by far the most common, hence worth mentioning first. Networks that have inherent issues can be seen to work differently with different versions of the same software or from device to device, so just because it worked before or works with a different device doesn’t exclude interference as a problem.
The following article(s) may help you.
If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network - Apple Support
Recommended settings for Wi-Fi routers and access points - Apple Support
Potential sources of Wi-Fi and Bluetooth interference - Apple Support
Check for Wi-Fi issues using your Mac - Apple Support
You may also find some help on this page, where Winston has collected some of the more unusual solutions to network issues.
