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?
If the gun is spring then it is most likely not automatic but if its electric it is most likely automatic.
That is mostly a matter of opinion.
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.
Anschutz and Remington 700 are regarded to be most accurate rifles in the world. NOMAN
Custom built
From a benchrest.
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 will need to define assault rifle, and where you live. A TRUE assault rifle is a machine gun, and transfers of them are tightly regulated by the Federal government. What most people CALL an assault rifle is nothing but a semi-automatic rifle, and in most of the US, does not require a license to possess.
It depends on the gun and caliber but most semi-automatic rifles such as the Ruger .22 are legal to hunt with in California.
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.