If there's one thing Mets fans can all agree on, it's that neither of these guys should make the team. Neither has been productive for the Mets and both hold terrible contracts as a result. While they are both free agents at the end of the 2011 season, meaning they'll be gone no matter what, neither has much of a shot of making the team. That said, one might be worth more than the other.
Manager Terry Collins has made it very clear that Castillo's only chance to make the team is by winning the starting second base job. Castillo has to get past at least three other players to do that: Justin Turner, Daniel Murphy and Brad Emaus. All three guys are younger and much better offensively, and if any of them are able to be even servicable defenisvely, Castillo has almost no chance.
Castillo appeared in just 86 games for the Mets last season, batting .235 with a misleading .993 fielding percentage. Brad Emaus seems to be the frontrunner to win the second base job right now, but many people think Murphy can raise some eyebrows in Spring Training.
As for Oliver Perez, Collins has said he will enter Spring Training as a starting pitcher but could make the team as a situational reliever. Right now, the only opening in the rotation is the No. 5 slot, and the Mets could certainly use a lefty there, but it's unlikely Perez and his 6.80 ERA and 2.07 WHIP from 2010 make it.
If Perez makes the team, it would be in the bullpen as a lefty reliever, which is about he only thing Perez has ever done well. He owns the big lefty bats of Ryan Howard, Chase Utley and Brian McCann in the NL East, but the Mets have also added Taylor Tankersley and Tim Byrdak on minor league contracts.
Right now, neither Perez nor Castillo has much of a shot at making the team, and it's just a matter of time before they're released.