It is hard to go wrong with the Holley for parts availability.
If you really are tuning a carb precisely, the Weber has more adjustments and variables to the play with. But it is not a quick learning curve, and probably is not needed on a stock /6.
The performance increase is going to be pretty darned limited (unless the present carb is just not working right). The cam and it's breathing are the limiting factors. Without going inside the engine, a bigger exhaust would be of more benefit than a different carb at this point.
What year of engine do you have?
And how did you come up with that interesting forum name? LOL
