I rarely ever have problems with my Fiio X3. It might freeze once in a while but the reset button works, and with these updates, we have a great product. I come to this thread and all I see are people complaining.
Different sounds, though not a huge upgrade. I prefer the FC300 but the dt770 is more comfortable and built better. If you have a good amp and only use them for home, then go with the DT770. If you want to use something portable, go with the FC300.