Durability and accuracy do not necessarily go together. Military firearms, such as the M1 Garand, M1 Carbine, M14 (OK, so the M14 is also full auto) and the SKS are incredibly durable. However, for accuracy, I am partial to the Browning BAR family of rifles. They are also pretty durable.
Impossible to answer as asked. Rifle, pistol, shotgun? What does accurate mean to you?
That is mostly a matter of opinion.
If the gun is spring then it is most likely not automatic but if its electric it is most likely automatic.
Anschutz and Remington 700 are regarded to be most accurate rifles in the world. NOMAN
From a benchrest.
Custom built
My favorite is the time x it is water proof and very durable.
It is often accepted the Heckler and Koch PSG-1 is the most accurate sniper rifle in the world.
You'd need to define your criteria by which you define "better". Most military doctrines dictate that riflemen fire in semi-automatic, and are supported by automatic weapons. Which is "better" depends on purpose, typically.
Too broad to answer. At what range? Rifle, rimfire, pistol, revolver? In general, a heavy barreled target rifle (most are custom builds) in one of the 6mm target calibers would be the most accurate to about 600 yards, but other rifles such as the .338 Lapua will be more accurate at 1500 yards.
You have to work up the most accurate load for your particular rifle. Each rifle will respond differently to changes in bullets, powder charge, seating depth, etc. What is an accurate load in one rifle may shoot poorly in another and vice versa.
Impossible to answer as asked. Factory or custom?