My .02:
Holley. Easier to find parts, easier to tune than the AFB (Edelbrock). The Demon's have a good rep, but I haven't seen one up close and personal, but I know that Barry Grant is a really good carb man--I would trust his work. The Predator: Junk. Hard to tune, hard to find space for and very unreliable. They were the hot new thing at hte tracks a few years ago, and disappeared shortly thereafter, while the Holley's just keep on going. Quadrajet: hard to tune for specific engine choices, more of a production carb--he!!, even GM used Holley's on most of thier real hipo stuff! That should say something!
Remember: at Generic Motors, QUANTITY is job one!