I've had pretty decent success doing good amounts of damage with two builds.
First for the PRIME, C-UAC/10 in the right arm with 180 projectiles (that is, 45 x 4 shots), 2 C-ER MLaser in the left arm. The amount of damage you can do if you avoid jamming the UAC10 is phenomenal. You want to engage from around 300-500M, hopefully aiming at whatever your assault buddy is aiming at.
Second for the S. A machine gun in each torso, two C-SPL in the right arm, C-SRM6 and C-SPL in the left arm, full jumpjets. Your role here is primarily to hide while the pokers poke. As soon as one of the lines break (either someone suicides into your lines, or one of your assaults grows a pair and draws some fire) pick an enemy on the edge of their formation and just assassinate him. Use your jumpjets, find a firing solution where you won't be targeted by more than your target and maybe one of his buddies, then go to town.
First priority is a rear torso, if that's not possible just eat his legs. Reason for this is that if you can open the lg armor, you'll explode the ammo there almost instantly with the crit-seeking MGs. As soon as your target and one other mech are focused on killing you, jump jet out. Rinse, repeat. Typical damage is 300-450 in an average match. A bad match where you choose your target poorly is 1-200 damage before you are explodified. In a good match where you can use most of your SRM6 ammo and a good chunk of the MG ammo, your damage will be in the 600-1000 range depending on how good your aim with the SPL is.
At first I had a lot of trouble finding my role and had many, many frustrating matches. But the key is to literally just hide and wait for people to be distracted.
Do not follow your light lance mates on a merry adventure, you aren't fast enough. Don't poke with the medium lance, they can take a gauss to the arm and still contribute in the scrum later - you cant. Just follow around your assaults like a good little pet, try not to get your legs run over, don't peek at all, then as soon as your assaults give you an opportunity just let loose like a small rabid dog. Bog is probably the best map for this, as the claustrophobic atmosphere gives you a good chance at isolating a heavier enemy mech and limiting the amount of fire you take in return.
Main drawback is that one mistake with your positioning and you're toast.
Edited by HansBlix WMD, 28 November 2014 - 05:16 PM.