You need to know that the AR-15 did not get as much attention as it should had have when it was first introduced for modern warfare pretty much the same with the M16. It was not that reliable when it came to the actual war and soldiers did not believe that the AR-15 was a good rifle at that time.
Time passed and technology grew even stronger that they were able to create a better AR-15. Today, with all its upgrades, the AR-15 is now a reliable weapon that both soldiers and marines put their lives on. It is now on the same level as the M16A2 and the M4. The AR-15 is a very accurate firearm and with that, it has become a popular rifle for a lot of people. With firearm collectors, enthusiasts and home defenders around, their weapon of choice is now the AR-15 and for a good reason. Check out this website https://en.wikipedia.org/wiki/Gun about guns.
The AR-15 was designed to be customizable and that is something that most firearm users look for in a rifle. Any firearm user would want a AR-15 because of how it can be customized to fit their needs. Sport shooters are in love with the AR-15 because of how it is today. The perfect rifle for target shooting and for a competition would be the AR-15, arguably. It is because the AR-15 is a very accurate firearm.
Basic training in any army will be holding a rifle and learning how to shoot it at distances of three hundred meters with only an iron sight. You will have an easier time firing at those distances with an iron sight if you have a good instructor and an AR-15 with you. With an AR-15 an a good instructor, you can learn a lot about shooting in just a few weeks.
Soldiers can do a lot of things with the AR-15 that they cannot do with their m16s and m4s; customizing is impossible for the two but is possible for the AR-15. There are a lot of custom AR-15 accessories such as QD end plate that you can use to build your own AR-15. Some people choose to buy while others choose to build their own AR-15. You can own a rifle that will fit you perfectly; that feeling when you cheek meets the stock perfectly. You can peer through your scopes with ease. Once you get all of these things perfectly, you are ready to fire.
Maybe it would be better if you try to buy instead of building but check out the factors first. There are advantages to buying an AR-15 but there are also disadvantages to it,
If you buy an AR-15 you will have an amazing rifle without any doubt. But when you build your own Ar-15 with complete accessories like AR-15 end plate, it will be a lot better than the one you bought.