Kemper user here (who is interested in switching to axe fx). I wanted to comment on this thread to mention what I see as the biggest differences between the kemper and the axe fx. I am discovering more and more how much control I like to have over different parameters in a tone. I am a huge fan of bands like Plini and Periphery, and bands like these have remarkable crisp and detailed tones. As I am putting in the work to make tones in a similar vain, I am discovering the downside of the kemper.
There are too many things out of the users control. Every single rig that exists is a simulation of a real rig someone else made. They can sound great and natural from the get go! But in comparison to the AXE fx, hands are tied in many ways. I find, in order to get closest to the tone I am going for, I actually cant even edit the Amplifier, EQ or Cabinet, because it diminishes the quality of the starting point. This is because it uniformly applies the same processing to every tone. Its not adjusting the tone like the original amp would adjust the tone (which the axe fx tries to emulate), its taking the starting profile and the kemper is adjusting frequencies in a single uniform way. SO, when listening with a fine ear you can hear a loss in quality from any adjustments that are made. If something sounds better from the adjustments, it means the starting point was not ideal enough. Once realizing this, it means the quest for ideal tone means finding the BEST possible starting point. But that requires sifting through all the free online tones, or paying for them. And I am not exactly excited about paying for tones on a product as expensive as this in the first place. And once a tone is found that is deemed a cut above the rest, it leaves a heavy burden on the 8 available effects blocks to attempt to get the tone to compete with something like the axe fx (in terms of getting a detailed tone seen by bands like those mentioned above). I use 4 studio EQs (or 5), a graphic EQ, a compressor, a noise gate and then if there is room some reverb at the end. And the sad bit of this detail.... the effects of the kemper are widely acknowledged as worse than the axe fx. The EQs, compressors and noise gates have done good by me, but I am just mentioning the general opinion held by everyone. And since the effects blocks are the last stretch to catch the tones up to the axe fx, this is not a good detail.
Here is the pro of the kemper. It certainly sounds more natural, in a rigs default state anyways. If you are not a knob tweaker, you will get pleasing and authentic sounding results easier out of the kemper. If you are a tweaker (which as it turns out I am), the axe fx is more ideal.
A personal frustration I have with the Kemper, is that each rig is a crap shoot in every way. Both in the quality of the profile, and the settings the uploader decided to apply. Not to mention, the kemper will never be able to compare with how the axe fx translates across different mediums, because every profile has some degree of a room impression. which makes the sound of it register as less upfront. and there is no way to do anything about this, it is intrinsic to the fundamental function of the kemper. This is just another thing inhibiting control.
One of the main proponents people have mentioned to me regarding the kemper is that "its a copy of a real amp, the axe fx is a companies impression of an amp". What they dont mention is that the controllable perameters literally pale in comparison. The axe fxs realms for control leave it in the kings seat for recording purposes.
Final thoughts. Sure, the kemper sounds nicer from a starting point and more natural. but if you want control over what you do, with the best translation over different speaker systems, go for an axe fx. If you really don't like putting work into your tone, then maybe go for a kemper. These have all been the thoughts from a kemper owner, not a salty axe fx owner.