As a 2012 Roubaix owner, all I can say is for the average cyclist who doesn't possess fantastic flexibility in particular, the Roubaix is the most important bike ever to be created. Specialized invented this genre of bike which has spawned many others like it from pretty much all top mfrs.
This is my opinion having been fortunate to own many high end road bikes.

Any of the years of Roubaix are good...newer ones are stiffer and have nicer paint jobs and many technical refinements.
Good luck.