For me the KPA is very, very unique, so there's no real competition from my point of view. It's the only tool, which is able to profile my own amps and put them into a small box. There are a lot of good guitar-devices on the market, but the KPA is revolutionary in many ways.
Effects are always a matter of taste, I'm really fine with a lot of the KPA-effects and I also like my effects and pedals from Strymon, Fulltone, Mad Professor, Okko ect. Some pedals sound very unique, too and you won't find them in any digital device.
Indeed, the Kemper is in a category all its own, and is a totally different animal from most anything else out there. The Kemper totally frees you from the limitation of having to use whatever model that is present in the modeler; if you can find a sweet amp that has that perfect tone, you can profile it and get 95% or more of that tone in the Kemper. And you can even enhance that tone with the Kemper deep parameters, making the profile possibly even better than the original amp (for example making its dynamics more usable with Distortion Sense and other parameters).
I have to say it is a bit strange watching the megathread on the Helix at TGP, and how many potential users are asking Line 6 to add certain specific amp models to the Helix, even before the unit is available for sale. Us Kemper users simply do not have that problem at all. It's really simple to add external effects of any kind to the Kemper, but it is far harder to get an accurate Dumble ODS or Friedman Pink Taco model into a Helix. I cannot imagine for a second going back to a Line 6 product.