It's not like Webb is over the hill. He's late-20's as well. You can have an opinion that Peavy is better, and he is most undoubtedly the better power pitcher of the two, but Peavy also pitches in a pitcher's heaven, while Webb pitches in a top-5 NL hitters park. Peavy has some health issues every so often, while Webb is generally healthy.
Peavy may be a better pitcher right this minute, but it's not by a long shot and I think Webb has probably been a bit more consistent over the last three seasons.
To each his own, and remember, my second favorite team in the NL is the Padres. I just think it's a bit more of a toss up, and at most, maybe 60-40 in Peavy's favor.
Webb vs. Santana should be just as exciting as Peavy vs. Santana.