I upgraded from Jessie to Stretch today morning. As per now, things are working fine.
There were problems during upgrade, as broken packages and dpkg interrupted. However, once installation was completed, everything is running perfectly.
I have KDE and GNOME currently running.
Let's see what happens in long run.
However, I have heard that Debian Testing is more stable than most distributions. Also, there were suggestions somewhere about using Testing is you have new hardware, as it provides newer kernel.