I have used and still own both brands for many decades, to be fair I've had more issues with Nvidia drivers, don't get me started on the mess Nvidia made when I had a 560Ti card and the many posts with lockups at geforce forums on the 4xx and 5xx series back then, yes they fixed it eventually but took nearly a year.
Having said that I would go for 390 over 970 if I was buying one right now(unless your PSU is weak).
I will say be careful of factory overclocked cards even new from retail stores, I've had a few in the past (mainly on Nvidia side) that were not stable at default factory OC levels, reducing OC fixed the issue, top brands like MSI, Asus etc you should be fine with factory overclocks in general.
End of the day drivers are not really an issue nowadays.