Originally Posted by Grasschopper
Ok I will be the first one to set up.
There is no point saying the Synapse is better in every way than the Roubaix because it simply isn't true. The fact is that they are both top notch bikes that are slightly different. The Synapse is a little stiffer in the rear end and a little racier in the front and (thus making it a little racier overall) but still is more upright than a CAAD8 or Six13 and more compliant as well. Plus it does a good job of absorbing the road vibrations. The Roubaix is a little slower in the handling and the rear triangle is a little more vertically compliant. This makes the Roubaix a little less racy than the Synapse but it does a little bit better job absorbing the bumps in the road and is just slightly more stable.
IMO both bikes are great and it all comes down to fit and personal preference. I went with the Roubaix over the Synapse for maybe not the best reasons, I could sell the slightly higher parts spec for more (since I only wanted the frame anyway) and I liked the paint job. To me that is what it came down to...I could have been happy on either bike.
I rode both of these back to back last night, and this was my exact observation. I went home with the Roubaix. It's personal preference for sure, but I was willing to give up a minute amount of handling for a significant gain in comfort.
Just try them both. They were different enough for me to tell fairly quickly which one I liked better.