I'm having a hard time choosing between the Auto Shotgun and the Fusion Cannon. You get the Auto Shotgun very early on thanks to a secret area and it remains useful for the rest of the game, especially with explosive shells. I'm not 100% sure, but I think it's also the first fully automatic shotgun in an FPS. The Fusion Cannon is Turok's BFG, plain and simple. Pull trigger,
everything dies. The gun looks cool and the explosion it creates is AWESOME! I'm gonna have to settle this with a coin flip.
Fusion Cannon wins!

Honorable mention goes to the Grenade Launcher (I'm a sucker for things that shoot bouncing explosions) and the Tek Bow, since it's pretty much Turok's iconic weapon along with the knife. And who doesn't love exploding arrows?