Just another person's opinion:
I've owned the Kemper, Axe-FX II XL+, AX8, HeadRush, and Helix.
Helix is the only "modeling" unit that I've kept... because the sound and flexibility (both studio and live).
I've owned most of the software amp-sim plugins (including Amplitube and S-Gear).
I don't even bother installing my software amp-sim plugins.
Helix is incredibly flexible, easy to use, and sounds better (IMO) than any current software plugin.
Not only good for electric guitar sounds; If you have a piezo equipped guitar, you can use "acoustic body resonance" IRs to dramatically enhance the acoustic sound (eliminating that smacky/quacky nature).
I've compared the Axe-FX II XL+ side-by-side with Helix. In this capacity, Helix (IMO) sounds more natural (less processed) than the Axe-FX II XL+ and AX8.
If you play live, Helix's form-factor is super convenient.
"Scenes" make it easy to make dramatic changes (instantly) with one foot-switch.
If you need to fly-in a bit of sampled audio, Helix foot-switches can send MIDI notes.
You've got brightly lit scribble-strips above each foot-switch (reminders when playing live).
What I like most about Helix:
If you can imagine something, it's quick/easy to make it happen.
For Helix owners, the Native version is $99.
IMO, That's a no-brainer.
At $400 (for those without Helix), it's a tougher choice.
I'm sure there will be discounts.