I will be honest here. I love my AX8 to death, but, I had the Amplifire before and it sounded amazing too, and I play with my friends Helix and it also sounds awesome.
The main reason I would personally never buy a Helix, or, to be more precise, I would always prefer the Fractal over the L6 stuff, is because of the "after purchase support".
For me the value of a product, specially a professional one, is 40% or less in the physical product and 60% or more in the customer support.
All firmware updates, how much Fractal hear the community, the infinite number of examples where a musician had a unit broken before a gig and Fractal helped them right away with a spare unit, etc, it is for me THE reason why Fractal gear is superior.
Also, the goal of a big company like L6 is put something out that is good enough and forget about it. Fractal (Cliff) in the other hand focus on incremental improvements just out of passion about it's own product. That mentality just proves that over time Fractal will always sound better because the amount of R&D on sound quality is exponentially bigger.
In that sense, an AX8 for 1400 is FAR cheaper for me than a Helix for 1200 since that on a Helix I am paying almost all money on the hardware, and on the Fractal, the hardware is like 400 and 1000 is for years of improvements and support.