I have a thing for the Stoner-Ares M-22A1, it's one of those few gems from the otherwise schwarbage Street Lethal. Yes, it's starts off with a low-ish accuracy of 4(6) and a recoil of +6, which is especially bad for heavy weapons because they suffer double uncompensated recoil. But you can easily fix that with the right accessories and you're supposed to be putting it on a vehicle anyways. It's a small price to pay for what you get: 18P AP -6 (getting shot by this gun is literally equivalent to getting hit by a stock Ares Roadmaster going at top speed), Full Auto, HMG ranges, a built in smartgun system and the option to use special ammunition types.
Honestly, it just shits on all the other heavy weapon options. Other machine guns? All virgins compared to the Chad MA Deuce. And before the minigun crowd utters a "but muh Vindicator", stop. My quality beats your quantity. Grenade launchers? More like teamkilling jackasses, am I right? Rocket Launchers? Half of them are one-use only, the other half are gimmicky and they all spend 2k or more per shot. Assault cannons? Sniper rifles with special ammo are better in every way. Laser weapons? Nice AP, too bad the atmosphere turns them into oversized laser pointers. Ares Thunderstruck Gauss Cannon? Not bad, call me back when it's got FA and a better damage profile.
My other favorite heavy weapon is my Roadmaster's ram plate, but I'm sure you know all about that.