I would suspect that aging components are more likely to determine the sound and hence which one is actually better than reputation is. Marantz when it was owned by Saul Marantz is a different thing than Marantz under the several companies that have owned it subsequently. I believe under Superscope, equipment was designed in the US and built in Japan, and is well built and sounds good. HK has had some ups and downs reputationwise, but they have always been designed with an eye to actually sounding good, and tend to have things like seperate power supplies for seperate channels, which is demonstrably a good thing, unlike incrementally lower distortion specs and lots of useless knobs.
So both recievers have the potential to be good choices. But quad recievers have a lot of stuff in them that costs money and produces heat, even if you are not using the quad facilities, which means that they probably aren't built to the standards of the equivalent powered straight stereo reciever, and all those extra components create more potential failure points. But who knows -- its impossible to predict.
So I think that only listening will tell you which one is better.
