For me there is no contest between Gysnc and Free Sync.
With every Gsync certified monitor you know exactly what you get.
And most importantly you get the full sync at 30 - Max refresh rate of the monitor (144hz). That is key!
You do not get the above with Free sync with every free sync monitor.
I don't even think there is a Free sync monitor out there that can do 30 - max refresh rate (144hz)?
The price difference between freesync and vsync is a massive point to consider though too.