I find both to be good (with spectre at slight advantage). However, if I encounter a group using mostly spectre's, I usaully love using the AR since I'm probably one of the few that uses it
if they have armour and are mid-range, Assault rifle seems better.
if they don't have armour and are up close, specter seems better.
Other than that they seem pretty similar for everything else, except specter allows some sort of stealth to it. Both will cost tons to get a decent amount of ammo for and both can basically tear anyone up in a 1v1.