Sig9 is all I've been using since I unlocked it. Before that it was rough times with the AK47.

I've tried to use the Pistols to get some extra XP by leveling them up, but I don't know if it is worth getting like 1/3 of the kills that I would get with the Sig9 in same situations.

Use the already set Lasered Stauger+Hi Cap+Snap Shot more often. It's much better than the sig9 on large maps.

I never wasted time on leveling guns, I just killed people more often with the better ones and felt great so continued on.