If we're doing semi-modular variants with arm-mounted weapons (you could even assign the Quirk "Modular Weapons" and specify only arm-mounted weapons...or just only have 5 crits per arm free, and one in the head or CT for balance), then my suggestions are:
Linebacker: 1.5t for three sets of Torso Spikes. Charge at top speed. Absolutely lethal against 40t and lighter 'Mechs with a 10/15(20) movement profile -- potentially up to 66 pts of physical damage including spikes, probably in the low-50s most of the time. That's hitting as hard as an Assault 'Mech on full alpha. (Plus, the spikes negate physical damage on the 'Mech that has them, up to 4 pts, which means you can prey on 40t and lighter 'Mechs with impunity...if you keep making your PSRs) Combine with TAG and a mix of lasers and after your first successful blitz, you'll be everyone's primary target numero uno.
NARC-buddy: 3t for the launcher in one arm, one or two ton ammo bin as well. Not quite symmetrical but close 'nuff. That leaves one or two tons for lasers in the other arm just for pot-shots. Run in, Narc, run out.
Recon: 1.5t in each arm for a Beagle and Guardian (one each side). Then a medium and small laser in each arm for pew-pew. Wave your arms around like a lunatic (or an Ostscout) when using your electronics. You can even go whole-hog with a TAG in the head, and no small lasers. Expensive in-universe, but fast and fun, and really useful when facing ECM bubbles or hidden/stealth units.
Rocketman: 2 RL-15s in each arm, plus a medium per arm, too: Anime missile cloud up to four times in the game. Crits prevent you from getting 3 RL-15s in each arm (only 11 free in the design), but you'd have no backup weapons if you did this, so oh well. If you really, really, really don't care about heat or back-up weapons, 6 RL-10s in each arm (okay, not enough crits, so it would technically be 6+5) and you can really pull off an insane, surprisingly long-ranged alpha-strike, for the low, low cost of +13 heat on the scale.