Long Story Short

Channel width plays a big role in Wi-Fi performance. Every wireless environment is different and you need to tailor your equipment to your needs.

With 2.4 GHz, increasing your channel width often isn't worth it, and you should stick with 20 MHz.

With 5 GHz, increasing channel width can improve performance, but there are tradeoffs. With 5 GHz, if you don't have to worry about interference and all your client devices support it, go with the highest width available.

Of course, the rules of thumb above won't always be best for you.