I'm going to jump in on this but keep it simple, Billy Beane is the best GM in baseball period... He constantly has to make moves around a small payroll, losing guys such as Miguel Tejada, Losing 2 of 'The Big Three' (Mark Mulder and Tim Hudson), and soon to lose Barry Zito in the offseason. Not to mention the countless others he couldn't resign or had to trade.
The brilliance here is how he manages to add young players but not just any young players, the right youngsters, who come in right away and are ready to take the field and compete. There are some good GM's in the league and I do consider Jocketty to be one of them, but if you asked me who I thought was the best to me, it's one of the easiest answers... Billy Beane.