Lets assume for a moment that the QC gets you a better capture with less work than the KPA. For those that this is the most important feature, I would say the QC is the product for you. I must say that this seems to be a strange one for me to understand. Even for people who have enough amps to want to profile a significant amount (and I can't imagine that this is a very big demographic. Most people I know have exactly 1 to 2 valve amps with the lions share having 1), how much of your time is spent profiling vs playing? Who cares if it takes the KPA 15 min to get as close to the original as the QC did in 5? Seems a bit like a nit-pick to me. To each his own.
For recording, I agree that having a USB feed is very appealing. Assuming that all the tones and efx that you want or need are in the QC, then it could also get the nod for the recording crowd.
For those that are bedroom bandits, I would say it is a toss up. Since the QC doesn't have a PC editor yet, the Kemper is likely a better fit. Sure, the on-device GUI is very nice on the QC, but is that really how a bedroom bandit would want to setup and modify their tone? I doubt it seriously. It is much more likely that they will want a nice PC interface. Perhaps when the QC editor comes out this category will change. The QC does allow 4 parallel paths which is superior to KPA's 2. If you are a tweaker, this might be for you .... but then again, if you are a tweaker, I would suggest the AxeIII Fx is by far the superior machine.
For live, I am just not seeing it at all. The KPA is simply a superior live gig machine IMO.
For those that want the greatest number of great tones and efx setups available to them, the KPA again wins handily. It simply has almost a decade of profiles to pick from in addition to numerous commercial profiles.
Finally, for those who just have GAS in a bad way every year, the QC is seriously a "must have". It is a very cool little box. If I didn't have to worry about putting kids through college, I might well have one just .... because!