Top 20 over the other 80, easily. Quality over Quantity all the way. The top of such a ranking contains games that would be unquestionably "unmissable". All-time classsics. Even when I would consider my personal list of favorite games, like those I made for Smeags's end of the year threads.
Now, taking that list, I think I'll still take my Top 10 over the rest, but it would be a hesitant choice. With less than 10, it would get really tricky. With any single library from any random console it's probably an easier choice though. Like say would I take my personal Top 5 N64 over all the others on the system, I'd easily say yes, let alone the Top 20.