Got to thinking about who I thought are the GOATS for MLB, NFL and NBA. Here are mine:

NBA/MJ

MLB/Babe Ruth although we never saw him play.

NFL/Jim Brown. This is the toughest one for me, but watching him on replays, he was just incredible. I saw an interview with him once, he stated when he was tackled he would get up slow, mainly because he didn't want the other team know he was hurt or tired.

Jim Brown and MJ retired in their prime.