As for baseball, Barry Bonds is the greatest player of all time. I know this'll offend you baseball purists who preach nothing but Babe Ruth, but Bonds is THE greatest player to have ever played this game. Argue steroids all you want, but the pitchers were no doubt juicing as well. Ruth never had to face consistent 95+ mph pitches.
Greatest quarterback? Toss-up between Manning and Brady, with Favre a very close second. The only reason I say Favre is due to his longetivity in the league, as he played in both the brutal days of little QB protection and today's pass-happy rules. Those that say Montana and Marino, I understand....but...Mont ana played on a virtual All-Star team. In those days, all but a few teams(with no salary cap) had absolutely no shot in getting to a Super Bowl. It was the same teams year in and year out that were good or bad. This is one of the reasons why the 49ers and Cowboys were so good for so long....so much amazing talent stacked. If Montana had played for the Rams, Lions, or Cardinals, he would've never sniffed the Super Bowl, if he even made the playoffs.
Today, ANY team can make it to the Super Bowl. Just in the last decade there were a handful of teams that made or won the Super Bowl for the first time in franchise history. There is much greater parity today than there ever was. Yes, the numbers are gaudy nowadays, but even bad teams can beat you on any given Sunday. Look at the Patriots. They are talked about year in and year as if they were some kind of NFL juggernaut, but yet they haven't won a playoff in game in 4 years. You still have to have a good team around you, and a QB alone isn't going to save you.