About two years ago I bought a Boss GT-1000 just for trying out... and finally sold my Kemper.
In the first two weeks I was disappointed about the GT-1000, because I didn't get close to the sounds I got from the Kemper. Then I loaded in some Celestion IRs: that was the missing part!
For me the GT-1000's sound is not better, but not worse than the Kemper. Of course the GT-1000's amps sound not like the "real" ones, but I don't care. They sound outstandig and that's enough for me.
With the Kemper it was a little bit easier to find the sound I wanted. But that was because I had enough time (4 years) to learn how to tweak sounds with this device. Now after two years using the GT-1000 I know how to handle this one and am able to dial in the sound as fast as I did with the Kemper.
The advantage for me is the smaller device, better GUI (on Windows and even Android with Bluetooth) and great routing options.
The Kemper is really great, but the Boss GT-1000 is great as well and fits better to my requirements.