Before this slides down the VS trail too far...
I've owned both. Actually two of both at one point or another. You can sound great with either one. Sit down, write down what you need and then comapre/ask questions based on that. If you just need to do XXX with certain affects in a certain order etc, the Kemper can do that. Both can nail pretty much any given amp tone, given a little effort. Also, what are you like? Do you like to dig into stuff or hate it? Do you like a simple interface without a lot of options, or a simple interface that if you want to, you can change things you never knew or wanted to know existed?
The biggest difference to me, because it is all modelling regardless of marketing speak, is flexibility. The kemper is not any more flexible than a POD, an Eleven Rack, G5 or any other unit out there. The axe is more flexible than all of them combined.
Second biggest difference is upgrade turnaround time and maturity of the product. Footswitch? Upgrades? Management? Just when I can't imagine it getting any better-something new spills out of Cliffs brains like so much zombie brain butter. I found myself always waiting on the Kemper to fix something.
Again, if you dont need all of that flexibility, you have a tough call. Though last I saw -the price difference was really making it as hard of a choice. THe KPA when I got it was around $1400, but it's near 2K now. For a few hundred more...just saying.