Was Griffey really the most popular player of the 90s? It depends on the fanbase you're talking about. I recall Nolan Ryan, Cal Ripken, and Mark McGwire being readied for sainthood at various times. Griffey was the bright new face of the game, but I don't think he really ever reached the iconic status that Ryan and Ripken did. I think maybe Griffey was #2 or #3 at all times, but never really #1 except with card collectors and younger kids.
The question of race in the Mantle vs. Mays and Aaron question is an old one. Blond-haired, blue-eyed Oklahoman who can run like the wind and hit the ball a country mile, comes to New York and becomes an immortal in the third golden age of that team even if he never actually truly met all possibilities due to injury and drink, I think it's inevitable that he'd be a living legend (and then a dead one) for millions of people across the country, especially whites. The other guys, better numbers, Mays arguably a better player, but that's not what the question is.
But as to OP, are we talking about investment now? Trout BC autos are stratospheric, and Miggy's 2000 TTr auto isn't far behind. I wouldn't touch either of them with an eye towards reselling. If I did, I'd go with a Trout gold ref or better.
Yes. Griffey is the beginning and end of the 90s.
A Nike Shoe line. Two Nintendo videogames. THE card that launched the premium card market.