The sniper rifles are all snipers but each is unique. The UNSC rifle is your basic rifle, which is good you need a constant or standard. The beam rifle is basically the same but doesn't need to be reloaded thus not requiring you to come out of zoom. The forerunner rifle is a one shot kill no matter the hit spot.

The rockets are all rockets. The Spanker is your standard but with vehicle lock on. The Decimator (as I call it, because it utterly destroyed everything in an area the size of a small island), is meant for total carnage. The fuel rod cannon is more of a precision rocket launcher with the ability to fire many rounds quickly and they bounce.

The precision rifles and AR's just need they're own area of pros and cons.