War Journal is very accurate, anyway :
out of 100000 MP kills (including Private games) I have 36k kills with Gnasher which I didn't boost at all.
Lancer, HB and Retro are equally 7k where I mostly boosted them to get "God At Arms".
Can't remember power weapons but I had most kills from public MP apart of heavy weapons but enough bragging.
On topic - play as You like.