First off, your APU is going to be a serious bottleneck to either of those cards. So unless you plan on upgrading to a more powerful CPU, it's a complete waste of money to buy either one of those. (A better option is the GTX 960 or R9 380.)
Now, if there was no bottleneck then overall I'd recommend the GTX 970. It is more power efficient and is a tad faster than the R9 390 at just below 1440P or lower. Meanwhile the R9 390 beats the GTX 970 at 1440P or higher resolutions.
But, the GTX 1070 and the RX 480 just came out. If your going to buy a new graphics card, definantly check those out as those are the successors to the R9 390 and GTX 970.