#1 Joe Nathan
Nathan is the definition of CONSISTENCY and that is why I give him the edge over Jonathon Papelbon. Papelbon is on a much better team, and so Boston will certainly win more games. However, they will also have much larger margins of victory on average than the Twins, thereby decreasing Papelbon's save opportunities. Minnesota will win most of its games by no more than three runs, giving Nathan an ample amount of save chances. And he has shown the past five years that when given the chance to save, save he will. Nathan can be counted on to have a Whip sub one, and ERA sub two, and rarely will he blow a save and almost never will he collapse and allow more than a single run. Never draft a reliever too early because really all he is providing for you is saves, and a chance to ruin your Whip and ERA with an implosion, and Nathan is surely your best bet.
Papelbon is the best young closer in the game today, and he plays for the winningest team in the MLB. In 45 regular season save chances in 2008, Papelbon blew only four saves, or a little over 90% conversion rate, which while good, is not stellar. 2008 saw Papelbon's ERA rise even more than it had from 2006-2007, and his strikeouts/9 innings were also significantly down. There is no need to worry about him in 2009, but it is possible that hitters are figuring him out, meaning Papelbon will have to make an adjustment.
Rivera, like Nathan, has shown extreme consistency over his years in the closer role. Unlike Nathan who has done it for five years, Rivera enters his 13th full season as closer of the New York Yankees. The reason Rivera is not ahead on my list of guys like Papelbon and Nathan, is only that his age could be a factor as it was in 2007, but did not seem to be in 2008. The Yankees as a club are much improved both offensively and as a pitching staff, and this will help give Rivera more save opportunities. A good candidate for 40 saves this year, though it could be one of his last 40 save seasons.
Ahhh...K-Rod in the National league. A league far weaker than his AL will allow his ERA and Whip to drop significantly. K-Rod will not save over 60 this year, and that I can almost guarantee, as the Mets are a weaker team than the 2008 Angels and he will not have as many opportunities. I do think that Rodriguez will still save in the area of 40 games and should help solidify a needy Mets bullpen.
Joakim Soria was a major force for the Royals in 2008. It did not matter that the club only won 75 games, Soria still saved over half (42) of those victories. It did not matter that the Royals has won of the worst offenses in the AL, Soria still managed to post an ERA of 1.60. And there is no reason he will not have the same or better numbers in 2009. Brad Lidge had similar numbers to Soria with more strikeouts, but how can you give the nod to Lidge, a guy with a history of mental implosions? Outside of K-rod, all the closers on this list, including Soria, are where they are because they do not walk batters, and they get outs. It can be seen in the tremendous Whips of all of them. Soria is a guy you can trust on your staff, he will rack of the saves, and not hurt your teams ERA or Whip (only 2 blown saves in 44 chances over 95% !)