I think all of the manifolds listed have their particular nuances and advantages.
Cliffords are the go to manifold on the racing scene, have better performance at higher Rpm’ when compared to an offy.
Cliffords can be found with and without water heat accommodations and with and without cast on nitrous bosses, but none will match up to a stock slant six exhaust heat box.
The 4bbl Offy does not perform like a Clifford at high ( for a slant) RPM, but does match up to a stock slant exhaust manifold heat box.
The newer Aussie speed manifolds have removable top plates so you can run either large 2 bbl carbs or 4 bbl. From what I have read a Clifford will out perform an Aussie speed at the drag strip. That does not mean that a slant could not be optimized for an Aussiespeed manifold and do well.
Hyperpac is the original slant performance manifold and certainly has the underhood wow factor. It obviously makes use of the legendary and historic mopar intake ram air tuning. With a carb fuel drop out at lower ambient temps is an issue.
For an engine that does not have huge aftermarket support it is amazing that there is a selection of intakes available. And I don’t think there is any one intake that has so much going for it that it would be the top choice for every slant build. But each build should be evaluated and the right intake chosen for it.
That said, I run a Clifford. I wanted the proven race performance and drilled the nitrous bosses for the mpfi.