Why should I chose a Holley instead of the Edelbrock?
Oh my, that question has started wars and toppled governments...
(Seriously, the "best carb" question tends to generate lots of "passion"...)
I'll do my best to be "objective"...
Advantages of Holley:
Lot's of people know about them.
You can get them pretty much as "big" as you'd ever want.
Parts are 'everywhere'.
Disadvantages of Holley:
They're simple (they don't have a dedicated part-throttle cruise circuit so they tend to not get mileage as good as a more finely "tunable" carb.)
Some of them like to "eat" power valves if the engine ever backfires.
Advantages of QJet:
Precise metering (they do have a dedicated cruise circuit) so they'll give better mileage than other brands of comparable capacity.
Variable CFM - they'll pass only as much air as the engine can handle, up to their limit.
Disadvantages of QJet:
Not as simple.
Once plentiful, but good, un-trifled with examples are getting harder to find.
Upper CFM capacity of 800 CFM (some models), others are 750 CFM - may not be enough for a large displacement/high rpm engine.
Not as many people know how to properly set one up (although many people "think" they do, which contributes to good carbs being effectively destroyed).
Parts sources are drying up.
I've got no direct experience with Edelbrock carbs, but I've "heard" from others that they're hard to get set up and don't run as well as a QJet.
I'm running an 800 CFM QJet on my car and I like it a lot.