UIC15 Mod2. Most useless weapon in the game. They wasted dev time making this weapon and adding it to the game, only to give it a lower fire rate than the Mk17 along with lower damage than the 420 rpm rifles. This weapon is a complete joke. The sad thing is, the gun actually looks really good and feels really good to fire, but because they're too lazy to change the base damage on this gun to something reasonable, the weapon just goes to waste. It would probably take all of 5 minutes to increase the base damage on this gun but no, that's just asking too much from Massive.
Least used? Definitely the L86. Does not feel like an LMG, does not fire like one, does not hit like one.
Can we just change it's classification and stats to an assault rifle? At least in retrospect of a game standpoint? This thing as an LMG is just painful to use, and wins my personal least used weapon.