Hardcore is the only way to go. I played last night w/ a friend who just got the game and hasn't unlocked hardcore yet and it is ridiculous how many times you have to shoot someone to kill them, I can't play it anymore, gotta stick to hardcore.
It's all about your ping. I usually have 3 bars and it takes an extra shot or two to kill someone. It's no coincidence that most of the people in the room with full bars are doing well.