my 0.02.... Ive had them all, axe fx ultra, ii, xl & 3. Axe 3 was fantastic but it took too long for me to dial in a decent and useable tone for me. Also I spent more time tweaking than playing. I found this to be the case with all my fractal units.
My kemper on the other hand took very little tweaking to get a tone that I could just go with. Sometimes the profiles are just right on the money and sound soooo good. As said before the kemper is only as good as the rig/profile loaded. It has great feel and response, the most like a tube amp in my opinion.
You have a tough choice man, both units are great. But ifI knew what I know now, I would havepickeda kemper from the beginning.
Hope it helps a bit. Cheers!