The SRM Adder

The SRM Adder is powerful.
Firstly, the adder is an extraordinary mech. It's a light that plays pretty much as a medium, without the drawbacks of most mediums such as size.
Adder is tiny, can mount any weapon combination that's out there due to its awesome omnipod selection, and can mount more weapons than any light mech without sacrificing armor. Awesome? Oh yeah.

And here's the absolute champion (at least for me): The Splat Adder.

Adder's hitboxes:

Purple is for central torso. Orange for side torsos. Green and Red - arms and legs respectively.

Here's the build I use:

I use the ADR-A variant with ADR-D arms for the missile hardpoints.

http://mwo.smurfy-net.de/mechlab#i=168&l=62dd026caf9d00e60cf4172f86af0a9f2ca8efc5

Now, I'll let you do the math yourself.
Small size + 4xSRM6 + almost 100 km/h = ???
You're right, the answer is PWNAGE.
And you can even mount a flamer there. There's no telling how many times I've shut down enemy mechs with it, and then just stood there, slamming them with the horryfing 50 dmg splat alpha until they explode.
Small size means you rarely get focused in the heat of battle. Why mind a tiny adder, when there are a Cyclops and a Direwolf right next to it?
Being generally invisible let's you do some horrible things to enemy mechs. And if someone decides to attack you? Again, you've got the small size, and you can also run at nearly 100 km/h.
Basically what you wanna do is stay behind your assaults/heavies and wait patiently for the brawling phase of the battle. Don't poke, don't run around. Stay hidden. Your size and your speed combined with the enormous DPS make you truly the king of the battlefield. Once the brawl starts, find a target, get in range, and fire away. If things get messy, get behind cover. Dart quickly in and out of the battlefield.

And that's all there is to it. 'Til next time.
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Other build variants:
The Streak Adder

Plays the same, just make sure you lock your targets. Way easier to deal with lights.