To me, the best GM in baseball is hands down Billy Beane of the Oakland A's. No GM does more with less than Beane. If you haven't heard by now, Beane stresses a "moneyball" approach to baseball his staff uses statistical analysis to evaluate players. Because of Beane, statistics like on base percentage and slugging percentage have become more valuable than batting average and stolen bases. Despite the fact that Beane is only given $50-$70 million dollar payroll each season, he consistently has in team in the playoff chase and continually finds ways to bring in top talent. Beane had the A's in the playoffs from 2000-2003 and again in 2006. Beane's detractors will say point out how Beane's Athletics have never made it to the World Series, which is true. But how many GM's have had this much success with such a minuscule payroll? Certainly not Dave Littlefield, Jim Bowden, Chuck Lamar.
But despite his success, Beane's most controversial move has come this season when he traded away SP Joe Blanton and SP Rich Harden even though the Athletics were only a few games out of playoff contention. There aren't too many GM's who would trade away two of his best starters when the playoffs are not out of reach. But Beane did it. He is smart enough to recognize that his team was not likely to sustain the same level of success that they had achieved during the first half of the season. So instead of standing pat and hoping that his collection of young players and retreads could actually pull this off, Beane traded his most valuable assets when their value was high for young studs (Adrian Cardenas, Josh Outman, Eric Patterson, Matt Murton, Sean Gallagher) who could help the Athletics for the next 5-10 years at very low costs. Beane exploited a trade market that had very few quality arms and was able to move two of his best for great talent.
While I can understand why A's fans would be upset by these moves, to me, this is just another of Billy Beane's cutting edge genius. Beane was able to recognize when the value of his players had reached his peak and he was not afraid to move them for the right price.