For anyone still on the fence between the Helix and AX8:
I own both the Helix and the AX8. Both are amazing at what they do. As it has been said a thousand times before. Helix is way easier to use, has more routing options and has a MUCH better screen. No arguing that. And sounds WAY better than Line 6's past efforts in this market IMO.
The AX8 amp sims and effects, for me sound a little better (not WAY better) and has more variety of sounds to choose from as your taste changes. Obviously option overload in some cases. Some people talk about Fractal having a head start in terms of amp models available but I disagree. Line 6 has been in the game for WAY longer. Some of the amps I will probably never use. But the effects are really nice.
With that said, when I got my Helix I started programming it for live shows and it was so easy. Had it up and running in no time. The AX8 however does take a bit more time to get up and running and to wrap your head around. But once you get the hang of it, it's a breeze. Especially with the computer editor. Forget about programming it via it's screen. It can be done, but the learning curve would be immense IMO! After a month with it, I could confidently say that I could make tweaks via the onboard screen at a show. No issue. Whatever one is best for you simply depends on your work flow and how much time you're willing to invest.
TIP: DO NOT and I repeat do not dial in your sounds with headphones. That may be common knowledge at this point but I thought that I'd throw it out there anyways because it wasn't for me. Get a PA speaker and dial it in at loud volumes. Studio monitors are OK but if you plan on using it live, use a PA speaker. What sounds good on a PA speaker will probably not sound good to you with headphones.
You can't loose with either of these units. What a great time to be a musician! Cheers guys and happy tone chasing!