For PvP I think if you've got an amazing connection and accuracy go with Hand Cannon (Since Bungie is buffing it) or the Scout Rifle, depending on the size of the map of course. If either one of those isn't amazing, go with an Assault Rifle. The pulse rifle also was buffed, but in the Beta the kick on it was ridiculous. Have to shoot them in the nuts or the third shot goes above their head. If you could find one with a significantly tighter shot group they may be viable.
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PvP- assault rifle it's the most consistent weapon in the presence of lag, and since lag can't be accurately predicted before a match, better safe than sorry. yeah, i'll get murked by snipers and scout rifles at long range, but if i stick to cover or only defend locations, i should do alright.
PvE- scout rifle imo, the scout rifle is the best weapon in the game, and when your PvP matches run smooth, it shows, but in PvE, you're going to have no lag(unless you're partied with a lagger) and it'll be headshots all day.
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