My post count at [url=www.df-21.net]DF-21[/url] exceeds my Massassi post count by a ratio of 2:1, so guess where my vote went... As for modded weapons, I know you can't really beat DF. While the game has the scripting for weapons hard-coded in, the graphical mods are excelent; who doesn't like the Black Whirlwind?
As for base weapons, my all-time favorite FPS gun is the original Stouker Concussion Rifle in DF. While it may deal only moderate damage, it always does EXACTLY the same damage, and the explosion chains to any enemy within the blast radius, allowing you to take out an entire legion of the Emperor's best troops in a single shot. (A Dark Trooper took 12 shots, though...). My preference for the Concussion Rifle is an anomally, though; I almost always prefer a sniper rifle to any other weapon (though I prefer energy weapons to firearms; my "ultimate weapon" would be an ASMD shock rifle with a scope)
Wake up, George Lucas... The Matrix has you...