One of the problems with this comparison is it's apples and oranges. The C'dale is a relaxed fit bike with a 20mm taller head tube and the BMC is a bike with a racing fit and normal head tube length, for a given size.

Which is best depends on your preferences. If you want or need a small saddle to bar drop, then a frame like the synapse is the better chaoice. With the BMC, you would be buying a too-big frame to get the desired bar height. Either that or you use a +6 stem instead of a -6 to gain about 20mm of bar height.