I had one of the first Helix units sold in the US.
Was using a Kemper at that time... and thought it sounded better than the Helix.
A lot of that was the fact that I'd spent months working with the Kemper vs. a few hours with Helix.
Sold the (first) Helix.
Over the next couple of months, as strange as this might sound, I couldn't get the Helix UI out of my mind.
It was actually FUN making/tweaking sounds.
At this point, I had the Kemper and Axe-FX II XL+... so I decided to pick-up another Helix... so I could have the three of them side-by-side.
First thing I did when I got the new Helix was to create an "acoustic" patch for my piezo equipped guitars.
Loaded an IR of the body resonance from a Taylor acoustic guitar.
The sound blew my mind. No more smacky/quacky/smacky piezo guitar sounds.
Used a small amount of EQ... and the sound was even better.
I'm not going to say it's a replacement for a well mic'd acoustic...
But for live... it sounds a whole lot better than it should.
To my ears, Helix was better sounding at this application (sounded less processed) than the Axe-FX.
My next hurdle; to create a nice dynamic crunch sound... in the ballpark of a 5150-III into a 2x12 with v30s.
About this point, I decided to create my own Cab IRs.
I had already done some Profiling with the Kemper... so creating Cab IRs seemed logical.
Cabs I like... mic'd the way I like.
That was the final kicker. Helix was now starting to sound like me (instead of vice-versa).
All the while, the UI was genuinely fun to use.
Helix was a keeper.
It was a hard decision to sell the Kemper.
It was the first device to convince me that great guitar sound/response could be had without tubes.
The Axe-FX is a great sounding unit... but I just didn't like the form-factor... or the onboard UI.
Axe-Edit (software editor) is a breeze... but maybe not the most convenient while holding a guitar.
Anyway... just my experience...
Everyone is different. If you can, try them all.
They're all capable of fantastic sounds.