M1A is pretty picky about maintenance. There are a lot of critical contact points that tend to shift. The gas system gets dirty and the volume changes, making the POI drift. I still have 2, but rarely shoot them because each shot is a countdown to re-bedding and cleaning. 5000 rounds and the barrels become suspect.
The AR15 is less needy. Bolt cam, and keeping the gas rings checked is pretty minor. If you have issues it is pretty easy to change out the bolt assembly and go. Barrels, especially the chrome lined flavor last a lot longer. Reloading is 1/2 as expensive.
I shot service rifle for many years, and on a fluke I started using the A2 with 1/7 twist in 1986 when they were adopted. There were very few 5.56 on the line, but that changed really fast. I have a place in my heart for the M14, but the AR15 platform is more shooting, and less rifle drama. I like to shoot, and in some ways I hate dealing with guns. Maintenance time takes away trigger time.
