I have had most of the faction scout rifles at one point or another, including crucible and vanguard. It seems all scouts take 4 head shots to kill regardless so the one I'd recommend the most is the dead orbit crypt dweller. It has the highest rate of fire of any legendaries and does 52 in head shots as apposed to the ~60 most others do. Nonetheless that's still 4 head shots one way or another. I got a lucky roll on mine and ended up with third eye, field scout and zen moment but the bought one is still worth while as far as any of the scouts go. Tl:Dr cryptdweller or visions of confluence are my two go to scouts. (Gheleons demise isn't too bad at all but shines in pve more than PvP)