Any ease-of-use advantage the Eidolon might have had went out the window the moment Battle Rifles got their muzzle velocity buffs back in 2014 - an assertion which the Oracle of Death clearly supports. Not even HSRs are any different amongst the 3 BRs. When using an AMR-66/Warden, aim for the top of your target's head and you'll get a headshot out to about 150m. Add in HV ammo and the distance increases to about 175m. Anything past that is beyond the Battle Rifle's effective range for most players, but if you can hit targets that far away just aim for the Dorito and again, headshot. BASRs are identical across all three factions - not including the Railjack which has no TR/VS counterpart. BASRs require more precision but that's balanced by the fact that you generally have little to no risk of dying from your target. You can fire shot after shot with impunity until they reach cover, and with the straight-pull attachment you no longer have to scope out (having to scope-out for the 2nd shot if they couldn't OHK was one of the major complaints used by snipers to get Nanoweave nerfed).