This discussion seems to illustrate an interesting point:
The more popular, longer-lived consoles typically can't be considered for the most consistent library because they were the ones that attracted companies looking to poop out shovelware to make a quick buck.
I may have to go with the Neogeo. When every game cost as much as a new console back in the day, the quality had to be top notch for people to shell out that kind of money for each one. No room for $200 shovelware.
It would be fascinating to see which console has the highest percentage of games which are generally considered to be "good". T'would be an arduous undertaking, methinks.
Neo geo CD has 100% arcade games no shovel ware at all you cannot get any higher than this console. sure same games compared to the main systems but less and without certain games.
The neo geo mvs and Neo geo aes had a very small % of gambling and quiz games 95% good games wich would give them 2nd place.
Sports games on the neo geo consoles are fun arcade games nothing in comparison to console sport games. Some of those sport games are really superb.
Furthermore pretty much all games were made by SNK themselves so crappy games are out of the question, a few obsecure non snk titles by sunsoft but than again they happen to make great and interesting games.
You could always take some uncommon systems into consderation like the capcom home console or the fm towns marty wich only have arcade games if I am not mistaken quite good ones at that also a 100%, but than again can you call these systems consoles? in my opinion not.