I use both and have for a number of years. Comfortable in both (more in FF, though). Full Garmin panel.
Smartcharts are really a great innovation, and the Garmin web application is now superior, but I still find the FF workflow more seamless, and the iconography and menu structures better, especially in a high cockpit workload. I haven't switched....yet...
Too bad you can't reliably run both at the same time on the same device (or at least I haven't ever been able to).
One thing is clear, though, Garmin is whittling away at FF's advantages, and at some point the scale will tip unless answered.