One of the best assessments :
From Line 6 ( Staffer)
zbadman, on 14 Oct 2015 - 01:59 AM, said:
Kemper is quite a different beast. It effectively samples the Amps one point, and then guesses how to make adjustments to that to give control. So, it is perfect at the exact point it was sampled, and less so at guessing alterations to that.
HELIX design philosophy is much closer to AxeFX2. They both sample the Cabinets, but they also model the sections that make up the design of the original models. So, they are much better at "guessing" the changes to an amp than a Kemper, but maybe they are not quite as accurate as the Kemper on the sweet spot that the amp was sampled at for the Kemper.
That's a fair assessment, although I'd say that every possible knob position in Helix could be considered a sweet spot, depending on how you dial in your amps.
Kemper's big advantage is the ability to sample your own amps—especially those that have unique characteristics that may be lost from serial number to serial number. And of course the gigantic library of profiles available. It's really a clever platform.
A good analogy might be the difference between a comprehensive Moog sample library (Kemper) and a hyper-detailed analog-modeled Moog softsynth (Helix). The sample library will have a ton of snapshots of a particular state of the Moog, and the filter and envelope knobs may work, but they don't necessarily behave exactly like the Moog's filter and envelopes. (Imagine applying an Akai or Kurzweil low pass filter instead of the Moog ladder filter—it may sound great, but it's not quite the real thing.) The analog-modeled softsynth may have fewer presets, but you can totally nail the nuance and behavior of every filter, envelope, LFO, etc., and even alter them in real time during a performance.
Both approaches have their advantages and disadvantages; it's more of a philosophy difference than anything. Regardless, one would have to really hate life to not be happy with a Kemper, AxeFX, or Helix.