Just my 2 cents, I bought a Kemper twice, got amazed twice for a few weeks then sold it back. The reason for that is that the Kemper basically uses the same signal chain for overdrive/tone on all presets and after some time, I could always hear a specific Kemper structure to the tone that's impossible to dial away. On the other hand the axe fx really models the electronic circuitry of each amp and that gives you a much larger tonal palette and less ear fatigue in my opinion. Both are capable of incredibly great tones, impossible to differentiate from mic-ed tube amps in a live situation. Of course, sound in the room at a rehearsal space will be better with a real amp+cab but I rather optimise for studio and live.