The Slingshot cannon, Scorpion, Spear Turret, and Grenade launcher have the longest range.
Energy weapons have significantly lower range than the above, but still fairly high.
The burst weapons excluding the HMG (Gatling, Autospear, Storm bolter, Avalanche, Dual/Quad SMG/Nail) have moderate range. Due to the guns converging on a singular point.
The flamethrowers have the lowest range, about 5-6 tiles. They're best used as a defensive measure, as they create a wall of flames that'll slaughter incoming zombies, but you probably don't want to drive though.
Just remember that damage dropoff for turrets is significant, a slingshot cannon can 2-3 shot a hulk with rocks, but will do little more than scratch it at max range.