It seems strange, but right now in the three major sports (baseball, basketball, and football) there is a major gap between the two conferences or leagues. Which sport offers the greatest gap?
Here are the baseball standings for 2006. While the American League boasted 5 teams with 90 wins or better, the National League only had one. The AL had 8 teams with 85 wins or more and the NL only had 4. If we move the bar down a little, the gap narrows a bit: the NL had 6 teams over .500 while the AL had 8. But putting that into perspective, every one of the AL's over .500 teams were at least 10 games over, while the NL had two teams that were 5 games over or less.
Even more to the point, the AL dominated in interleague play 154-98, a .611 winning percentage that would have won every division in baseball. And while the Cards won the World Series, I don't put too much stock into a short 7 game series. The Cards went 5-10 in interleague play. If they switched place with their Missouri neighbors, they would have ended up in the exact same place in the AL Central: last.
The season isn't over but it's clear which conference is better at this point. The AFC has 4 teams with double digit wins; the NFC has one. Put another way, no division leading team in the AFC has more than 4 loses. The NFC has three such teams.
And it gets worse. The AFC has 8 teams that are 8-6 or better; the NFC has 5. The AFC has 12 (out of 16, which is 66%) teams that are .500 or better. The NFC has 7. There is serious talk of a 8-8 team making the playoffs in the NFC. 10-6 should be enough to do it in the AFC.
Interconference games are the reason for the disparity. The AFC's record against the NFC is 38-22, which is about a .633 winning percentage. Put into perspective, that percentage would win the NFC West, and would be a tad behind the Saints and Cowboys for bye weeks.
Let's take a look at the NBA. The East has only 4 teams that are over .500. The West has 7. If we make the rules more strict, the West has 7 teams with a better than .600 winning percentage, while the East only has 3. The West also has 4 teams with a better than .700 percentage, while the East has none. Oh did I fail to mention that the Atlantic division leading Celtics are 3 games under .500?
The interconference rate in pretty high as well. I might be off by a number of two, but the West is beating the East 84-52, which comes out to about a .608 clip. A team with that percentage would be tied with Cleveland and a tad behind Orlando for the second spot in the East. They would also be tied for 7th in the West.
So based purely on interleague and interconference percentage, it would seem the NFL has the greatest gap between its two conferences. We'll have to see where everything ends up in the NBA, because the season is barely 25 games old. The NFL is pretty set, since most teams of the interconference games are finished.
Of course this analysis isn't completely acurate since we need to take schedule into consideration. We also have to look at home/away records. But as it stands right now, the winner of any of the better leagues or conferences is clearly the best team in its sport.