This topic came up at the Flushing University message boards yesterday and I first weighed in over there. The Mets bench is better this year than it was last year, but I think that Philadelphia has a better corps of reserves.
The Mets do have the advantage at two spots. Miguel Cairo stinks; I would definitely take Alex Cora over him. I would also take Jeremy Reed over Eric Bruntlett, but the difference between the two is mostly on the field and not at the plate.
As for back-up catchers, I would take Chris Coste over Ramon Castro, if I had the choice between the two. Coste has out-hit Castro over the last three seasons; perhaps the only season where Castro was clearly better offensively was in 2007. Castro has a little more power, but Coste stands up well offensively otherwise. I don't know if either one of them is particularly good defensively (I happen think opinions on catcher defense are extremely subjective), but they did throw out a similar percentage of base-stealers last season.
Greg Dobbs and Fernando Tatis are an interesting comparison, but Dobbs is better defensively and has been a valuable bench player for the last two seasons. Tatis was wonderful last year, but I'm not ready to proclaim that it wasn't a fluke. Put it this way - I'm glad Omar Minaya signed Tatis to a one-year deal instead of the two-year specials he has been giving bench players over the last few years.
Gary Sheffield has had a borderline Hall of Fame career (if you don't believe he was on steroids at any point, that is). But right now, he doesn't belong in the same conversation with Matt Stairs. I think Stairs is one of the most underrated hitters of the last 20 years and he's an asset to any bench he sits on.
Stairs can't field, but that just puts him in the same category as Sheff defensively. He remains very dangerous against right-handed pitchers and could still be effective as the dominant half of a DH platoon in the American League. Even at 41, the guy is a mortal lock for 10-plus home runs if he gets 300 plate appearances against righties. He's still patient at the plate and still draws walks - an asset for a pinch-hitter, despite what conventional wisdom might say.
From my count, the Phillies are better at three of the five bench spots and better on the bench overall.