I've ridden older models of both, so it may not be relevant now, but....... I thought the Roubaix was a little more upright out of the box than the synapse and a touch more comfy/cushy on the ride. That said, I bought a used '13 Synapse, it doesn't quite completely isolate you from the road, felt a little more "spirited" when riding. slightly sharper handling, I felt a bit more connected to the road. both are great bikes though. You wouldn't go wrong with either so test ride both and figure out which fits your needs best. as I get a bit older I've considered revisiting the roubaix, but I'm very happy with the synapse after two seasons, it serves my needs well.