I have little idea who the greatest ballplayer I ever saw in person was, largely because my memory is terrible.
I was at that 7th game of the 1975 World Series. Morgan and Yaz, of course. Pete Rose tied the game (I see, reading the game notes) in the 7th inning. I remember the pop out to end the game, but that's about it.
I was at the Vida Blue vs. Sonny Siebert game. Blue was an amazingly dynamic pitcher, but not for long enough to be the greatest pitcher I've seen, as I have been to a couple Pedro games along the way.
I had season tickets to the 1990 Red Sox. Roger Clemens, Lee Smith (whose acquisition prompted the ticket purchase), Wade Boggs. And Joe Morgan!
Oakland had Eck, Rickey, Jose (and Ozzie) Canseco, Dave Stewart, and the immortal Harold Baines. I know I saw them, in the playoffs. (I probably still have my unreturned World Series tickets from that year somewhere.)
It was not an amazing season for AL players, in terms of "greatest ever" folks. There were a few.
Griffey, Jr. was among those I got to see. I've seen ARod. That Ortiz guy once or twice. Got to see Jacoby, who we all thought was going to be great and Mookie for whom we still have great hopes. Nomah.
Easier to tell you the greatest players I ever met, as it is both a smaller number and more memorable (to me). Met Pete Rose, Johnny Bench, Sparky Anderson, and Earl Weaver in one evening, along with Derek Sanderson, who had a great swing. Met Bob Uecker and George MacDonald, the King of Baseball, in the same evening as the others.(Billy C was not as big a draw for me ass the first five names.
I had no idea at the time who "the King of Baseball" was. I knew from the Clown Prince and the Sultan of Swat, but the King? Not so much.
I met Teddy Ballgame and I think he's probably the single greatest player I ever met, but I got some quality time in with Eddie Waitkus. And Dave Engle is probably the best baseball player I was ever on the field with as a teammate. No, not too great; he was just the greatest of my dubious baseball career. His first two months of 1984 were amazing, but something happened and he never got back to that.