I would go with the R9 390 too - the GTX970 is more useful in SFF builds were the shorter cards and lower TDP are very useful in comparison. The G-Sync argument also is all fine and dandy but there is a significant premium to be had on the monitors,and Freesync is significantly cheaper,and as time progresses the tech will mature too. Remember,G-Sync has been out longer and had its niggles at the beginning too,but quite a few companies are now introducing Freesync monitors.
The fact that G-Sync needs a custom FPGA,means the cost probably won't be as easy to decrease over time. You are also locked into G-Sync too - since AMD and now Intel will support Freesync/adaptive v-sync,there is more chance Nvidia might support it at some point,than AMD or even Intel supporting G-Sync themselves.
Remember,Freesync is just the AMD software interface for adaptive v-sync which is a part of a VESA standard.
Regarding uarchs, uarchs have strengths and weaknesses,you can't just say one is more advanced than the other,otherwise its just parroting marketing bumpf.