318 for general use.
Make it easy on yourself.
Use a carb with smaller venturies and throttle bores. It will get on the main system at lower throttle position and be easier to tune.
Whether its a Carter design or Holley really doesn't matter much IMO. Use a spreadbore if the intake is really meant for spreadbore.
I personally think the prices charged for most new carbs is 'market will bear' rather than cost plus profit. And the prices some folks are asking for used carbs is often based on current retail, but sometimes you can find more traditional pricing. Of new, I think the new Holley 'Demon' which combines Carter T-quad design with squarebore pattern is most likely the one I would chose for all around use.