I personally would love to see the Doom cruiser as the mascot, even though it's probably too rare in-game. I love flying that ship when I can get my hands on it.
Onslaught and hound, like many have mentioned, are distinct enough and 'ship' enough (if that makes sense) to be a good mascot. I was considering the Dominator, but it's a bit too...plain to be a mascot. I do like the idea of the Sunder, which is also a unique and iconic ship.
If you want to impress people, you got to have a heavy metal war machine that can kill everyone and fit in with monster trucks, guns, and hard rock concerts. Onslaught does that.
Onslaught also has Burn Drive. You got to have flames, big flames.
You know, it would go faster if we painted it red...