If you're between those 2, I'd go with the Synapse 105 as it's more of a road bike and I'd want minimum 105 components.
If you're in that price range, I'd have a look at Giants. They're well priced and you often get more bike for the same price as Cannondale or Specialized.
For a similar price to the Diverge Comp, you can get a Defy Advanced 2 here
http://www.ridleys.com/product/giant...2-264155-1.htm with a full carbon frame and 105 components while still keeping that endurance frame like the Synapse. Your bike choice will probably depend on whether you want to do more road biking or some gravel riding too.