The main problem with Holley four barrels is the needle and seat. They are at the top of the bowl and exposed to air. They will dry out after sitting the winter. The next spring they will not seal when the engine is started and the floats will overflow. New needle and seats every year.
A Quadrajet carburetor has the needle and seat in the bottom of the bowl. It is covered with gasoline all winter and remains moist. If you use a fuel stabilizer the needle and seat works fine the next spring (and many springs after).
Rebuilding a Holley is a crapshoot because the metering block can get plugged with debris or varnish and there is no way to clean it out unless you remove the welch plug.
Plugged metering blocks are the main reason why there are so many used Holley carbs sitting in the junk pile!
A Holley carburetor will shoot too much raw fuel into the engine every time the throttle is opened. This washes down the cylinders of oil, will cause premature wear to the rings and dilute the crankcase/oil with raw fuel. The diluted oil will wipe out the cam lobes on a flat lifter camshaft.
A Quadrajet or Edelbrock carburetor has a cup style accelerator pump with a slot in the pump bore.
Fuel will bleed off (back) into the float bowel when the throttle is opened slowly.
Smaller pump shot.
If the throttle is opened quickly less fuel will bleed off into the float bowel.
Larger pump shot.
Holleys have a positive displacement accelerator pump and once the pump shot volume and duration are adjusted (pump shooters and pump cam) the same amount of fuel is shot into the engine whether the throttle is opened slowly or quickly. This makes for a very rich air/fuel mixture when slowly maneuvering around the docks or at the launch ramp.
The square bore Edelbrock has twin float bowls and twin needle and seats and is the same carburetor (Weber four barrel/Carter AFB) that Mercruiser used when they could no longer buy Quadrajets from GM. It is important to realize that Mercruiser chose the Weber Four Barrel over the Holley Four Barrel for installation on Mercruiser Sterndrive engines for reliability issues.