I haven't ridden a Synapse. I'm not particularly overwhelmed by the handling of the "civilian" Domane, but the ride sure is smooth. Until the Solace came along, Scott's idea of an "endurance" bike, the CR1, was an all-road workhorse of a race bike. Snappy, neutral, and forgiving handling, a ride that's informative but not harsh, clearance for fatter tires, and a cockpit geometry that isn't too tall and short make this one of my favorites. The design has been around since 2009, and it's only seen small changes over the years.
The CR1 runs a bit longer than the Domane, so if you're on the boundary of two frame sizes, seriously consider the smaller one.