i used one of the DLC ones personally cause it's awesome, always able to lvl up because it has no ammo.
Laser Cannon: my main, no ammo means i can lvl it anytime i find one and any upgrade cube, i pretty much only use this purple laser of doom.
anything else: i don't really use other weapons lol, i keep on me just what i'm lvling up, after i max lvl a weapon, i usually start on assault rifle and heavy machinegun, then move onto sniper and shotgun, then i grab just whatever happens to be around i don't really use the other weapons at all, on my first game and then achievement whoring after it i upgraded those that i needed to get specific kills with to max and then used them for expediencies sake.
i like to get heavy machine gun and assault rifle maxed for later lvls where i can't use energy weapons like on vipers because i can't use the cannon on them, and sometimes it's just easier to fire smaller guns and they have plenty of ammo around. i upgrade snipers and shotguns because of the sniper lvl it's easier with strong sniper rifle and the shotgun also for the viper lvl and for larger walker enemies (non-gaint super boss things)
I am epic ~desu~
95.63% 1903/1990 cheevos gotten 12-03-02
I exclude games and DLC i don't own. (-3 games, -3 DLC)