Both the M1A and the M1 Garand have a reputation for being rugged and reliable weapons. I’m not aware of any major difference between the two with respect to long term reliability. I wasn’t able to find anything poking around on google either. Most of the comments are that they are both reliable, and long-term reliability isn’t generally a factor in choosing one over the other.
As for ball rounds, that dates back to the musket days. The standard round was the round ball, and it was very much round, spherical, and shaped like a ball. The name stuck, even when rounds were no longer ball-shaped, like the Civil War era Minie Ball, which is more conical than spherical. Calling it a “round” also stuck, just as the phrase “lock, stock, and barrel” still refers to the whole thing even though rifles don’t have locks (flintlock or caplock) any more.
Once you had conical rounds being called ball ammo, there’s no clear dividing line where you should stop calling them balls and start calling them something else.