I guess whatever you buy there's no guarantee they wont nerf it at somepoint so maybe best to get wat suits your style. I like the scout rifle (I realise I'm in the minority on that) but I find I can pretty much use it to snipe on most occasions but it still has enough ammo and good hip fire so I can use it up close too. I'm not sure about how the attack vs impact works but it seems to me the damage done in PvE is some multiple of these but in PvP it's just down to the impact. So in PvE you need to be looking at both numbers, that's my guess from what I've seen so far but I can't find a definitive explanation of the damage calculation anywhere so this is all guesswork!