They're really different bikes. The CAAD frames use to be much higher in Cannondale's range, and it's a very lightweight stiff, true racing frame. The Trek 2 series has a taller head tube resulting in a more upright riding position, so it probably will feel more comfortable. If you'd like to compare the 2.3 to something from Cannondale, then you should probably look at the Synapse, which has more relaxed geometry.