VeloNews did a comparison test of seatposts a couple of years back. If you search on their website, you might be able to find it.

I've got two aluminum bikes - a 2009 CAAD9 and a 2012 Allez E5. Both take 27.2mm seatposts. I've got a Nashbar carbon seatpost on the CAAD9, and have another that'll go on the Allez probably tomorrow. I got the first one because it was the cheapest zero setback seatpost I could find, and the second because I liked the first one. The feature I like isn't the carbon part - though it is pretty, and might take some buzz out of the ride - but the clamp. It clamps and adjusts via two allen bolts that are accessible from the bottom. Getting the angle just right is easy, where it's a bear on some other seatposts like the stock Specialized one.