Much as I love the intercepters (and the anti-son-of-a-***** machine that is the Erinyes), I gotta hand it to the Pegasus.
I love the design, and when I flew it, I fell in love. Beautiful flight characteristics. In a level FREDed for TAGing, nothing beats the thing. And there's something immeasureably cool about being mostly invisible, especially when you have to deal with freakin' AAA beams.
Aside from the Pegasus, definitely the Erinyes. Or the Perseus, if I want to dogfight instead of own everything in one pass.