As someone running Shackled City, I think that Age of Worms is better.
The staff knows what it's doing this time around, and have provided a ton more coverage and options leading to richer possibilities for the GM, while at the same time, making the GM's job of converting, a lot easier and hassel free than before.
It'll be very interesting to see if they do a compendium of this book because Shackled City is great (on week ten now) but because of the downloads and Dragon magazine Wormfood articles, an Age of Worms book would be evern bigger and more expensive. Something the market might not be able to support. Might even have to be cut into two books or one hardcover book and a PDF download for support. It'll be interesting to see what happens.