My opinion I don't care what spec i play as a sniper as long as its top. learn to be flexible its going to happen a lot. Marks will shoot up to be the best spec once in awhile then Lethality will do the same. I played both specs and i like the mobility of Lethality for ops while doing 1500 damage + to HM Denova. But i could also play marks and see those high bursts, yea i do less damage over a period of time but its still fun... If your really want to be competitive to any other sniper then you must play where ever the game might lead you.
