Stormfire, Stormfire, Stormfire- only downside was limited ammo. That said, of the more "conventional" guns-
The Excal's quad Tachs- the WC3 /4 tachyon guns were great- the refire rate was good, the damage was high, and the bolts moved. The only downsides were range and power drain- but anything you attacked usually died before your capacitor went out, and if you could slash and burn in a fast fighter or wade through a barrage in a heavy fighter to get in close, you could shred pretty much anything. (that said, I thought the WCP tachyons sucked- they fired far more slowly)