The AR-15 rifle resulted from design work by Gene Stoner and first produced by Armalite about 60 years ago. Submitted for US Army trials, zero interest resulted. All patents and production rights were acquired by Colt, and with far superior weight in political support the M16 rifle won military contracts (first by the USAF, then by US Army and USMC), just about the time that the US was becoming seriously involved in Vietnam.
Most US military units were still in the decade-long process of replacing the M1 Garand and M1 Carbine with the new M14 rifle, a program that was never fully accomplished. President Kennedy was reportedly upset while visiting West Germany to see our troops guarding the Fulda Gap with M1 rifles about 5 years after the new M14 was adopted as the standard service rifle.
I trained on the M14 rifle in 1968, with a required familiarization training on the new M16. I was not impressed (reliability or accuracy). Went to Vietnam in 1969 and was issued a new M16A1 (forward assist mechanism, a few minor refinements), and I remained unimpressed. The common description among the troops was "You can tell it's Mattel, it's swell" (1960s advertising campaign for Mattel Toy Corporation).
In the following half-century I have owned several. Colt SP-1, DPMS AR-15, Rock River Arms, even a Colt M16A2 (LE special purchase, contract overrun for a state agency contract, tax stamp required, of course). Despite the remarkable longevity of military use, plethora of producers on several continents, and massive popularity of the basic design, I remain unimpressed.
Best advice I can give you is to make sure your hearing protection is top notch, those things are incredibly hard on the ears.
For personal defensive use I will continue using a 1943 Inland (General Motors) M1 Carbine .30 caliber. For serious rifle shooting I will continue using a Springfield Armory M1A National Match 7.62NATO.
Have what you like. Enjoy what you have.
Did I mention that I like S&W and Colt revolvers, and regularly carry a .45 caliber M1911 pistol? Haven't been to a Tupperware party for many years.
Tongue firmly in cheek here.