Best Generic Gaming System?
As swordchucks insinuates, this comes down to a number of preferences:
Fluffy vs Crunchy,
Completely Genre Agnostic vs Genre Adaptive (some systems build the rules to be for ALL genres, you just flavor the skills/abilities, whilst some have source books which COVER all genres.)
Strongly built-in Flavor vs Completely Story Agnostic,
Class/Archetype-driven vs Classless,
Dice vs Diceless,
etc.
You'll want to identify those preferences for yourself, and that will either answer the question for you, or narrow-down the answer.