I've been an Axe user since July 2008 and picked up the AxeII last summer. I also own an 11r and pretty much every plugin, modeler and some great amps (nothing "vintage"). I absolutely love the MTS mods, especially Salvation stuff and JF, although my favorite mod is still the stock Plexi - it really has a great "crunch.". The Axe sounds great through the Atomic FR, but when ABing the 11r with my Plexi reissue, I thought the 11r sounded better than the Axe. This just happened this week after thinking I haven't played through the 11R in months and thought to give it another listen.
In all honesty, I'm pretty tired of "tweaking" the Axe, especially after every firmware update - Cliff changes the basic sound of the models, so you have to update 384 patches. He also doesn't really say what he changed, so you have to "use your ears" to reset your old patches to work the new firmware. I'm also tired of hearing how each firmware is "a game changer" and "the best". At this point, I'm not sure how you can even tell what sounds better since there is no easy way to compare firmware versions.
In terms of FX, I still prefer my Line6 M13 to whatever is in the Axe. Yes, the Axe is way more flexible and you can route fx and use controllers, blah, blah, blah. Really, how many people need to do all that? Most pro users are using it either for the Axe's FXs or as a backup to their main rig (Alex Lifeson for example). Not sure how many people replace their tube rigs with an Axe.
Does the Axe sound great, work great. YES, but if you prefer to just play rather than Tweak, the MTS may be a better solution.
I'm very interested to hear the Kemper in person and see whether the amp models sound "like" my amps or Exactly like my amps (indistinguishable). Although I thought the Axe sounded much better than Line6 modelers, such as the Vetta or HD500, as well as Amplitube, GTR, GuitarRig, Revalver, etc, it still isnt exact. There is still a fakeness about it I can't explain, but becomes obvious when you play a real Plexi then switch to the Axe.
It is still an amazing unit and still the best out there.
But let's just say the Kool-aid has worn off on me.