I've eaten at both a number of times, and MSS wins hands down. GN buffet is really tiny. I only eat at GN when I'm not really all that hungry, and just want a quick bite to eat.
I think that they are pretty close for quality - but MSS wins for price.. GN has a better dinner - but it is not as good a value a MSS. MSS wins for breakfast - quality and price. But if you really want a big and good breakfast - Hash House at Plaza