In my personal opinion, the Helix is a vastly better option. MAJOR CAVEAT: I have never owned a Fractal product, this is based on my opinions based on product information, youtube videos, and my own experience owning a Helix.
The main basis for my position is that in my opinion, Fractal does not give a poopie about bassists. The originally only had an SVT model, and in 2014 they added a Orange AD200 model, a Cali 400+ model and a custom fractal model, and to my knowledge they have not released a bass amp in the four years since. The Helix launched with more amp models than fractal, and has also added more models in future releases, giving the Helix 13 amp models compared to Fractal's 5. I believe both units have a similar number of cabinet models, and based on the sounds I've heard, both are of very good quality.
Another huge advantage is that the Helix has dynamic DSP, where your DSP is not category bound, while the fractal places limits on the number of each type of effect that you can use: Effects list - Axe-Fx II Wiki
The Helix places no restrictions on effect categories, while placing some limits on amps and cabs (which you would probably run out of DSP before hitting).
With the AX8, you are limited to a single amp model and a single cab, where with the helix, you can have up to 4 amp models, 4 cabinet models, and 4 IRs loaded (depending on the DSP of each amp). I've made a Nolly-esq patch on my helix where I run a clean bass amp into parallel mic'd cabs, and run a 5150 into a different set of parallel mic'd cabs. This would not be possible on the fractal, as you are limited to 2 cabinets per patch. With regards to effect types, you also have no limits on the category. On the Fractal products (even the FXII rack unit), you are limited to two drive pedals. On one patch with the helix I did, I had a B7K model as an always on tone shaping, then had 5 different distortion pedals on a parallel path along side a clean blend (RAT, TubeScreamer, Bass Fuzz, etc). Then at rehearsal, I was able to experiment with different distortion settings to see what worked best with the guitars. This would not be possible with the Fractal products.
With regards to Fractal having better sound quality, I think that comes down to individual preference. Having never played a Fractal product, I don't feel comfortable commenting on the sound quality (for bass). From what I've heard, the Fractal is at the same level or slightly better than the Helix products. However, with the Fractal, you're sound is basically limited to the thunderous tube head amps. If you wanted a Pearce or GK like sound, you'd have to spend a lot of time trying to come up with a patch to emulate it. When it comes to guitar, I think the Fractal definitely has an edge over the Helix (in terms of sound quality and amp selection), so if you play a lot of guitar that's something to consider.
If Fractal would actually start caring about bassists, I would love to get a Fractal product and do a proper comparison between it and the Helix. The majority of my dislike for Fractal is not because of the amp models or sound quality, but because of their attitude towards bass. Its hard to justify spending 1-3k on a piece of gear (depending on AX8 to Axe FX III + foot controller) when you know their entire R&D budget is going to go into guitars amps/effects and you might see a token update in 3-4 years, especially when a competitor provides excellent updates for bass. If all you do is play a straight "bass -> SVT model -> cab -> out to board signal", I think the Fractal would be a great choice, and might even sound better than the Helix with the same signal chain. But if you like using lots of effects, or like having variety in the amp models, I think the Helix definitely comes out on top.
The main basis for my position is that in my opinion, Fractal does not give a poopie about bassists. The originally only had an SVT model, and in 2014 they added a Orange AD200 model, a Cali 400+ model and a custom fractal model, and to my knowledge they have not released a bass amp in the four years since. The Helix launched with more amp models than fractal, and has also added more models in future releases, giving the Helix 13 amp models compared to Fractal's 5. I believe both units have a similar number of cabinet models, and based on the sounds I've heard, both are of very good quality.
Another huge advantage is that the Helix has dynamic DSP, where your DSP is not category bound, while the fractal places limits on the number of each type of effect that you can use: Effects list - Axe-Fx II Wiki
The Helix places no restrictions on effect categories, while placing some limits on amps and cabs (which you would probably run out of DSP before hitting).
With the AX8, you are limited to a single amp model and a single cab, where with the helix, you can have up to 4 amp models, 4 cabinet models, and 4 IRs loaded (depending on the DSP of each amp). I've made a Nolly-esq patch on my helix where I run a clean bass amp into parallel mic'd cabs, and run a 5150 into a different set of parallel mic'd cabs. This would not be possible on the fractal, as you are limited to 2 cabinets per patch. With regards to effect types, you also have no limits on the category. On the Fractal products (even the FXII rack unit), you are limited to two drive pedals. On one patch with the helix I did, I had a B7K model as an always on tone shaping, then had 5 different distortion pedals on a parallel path along side a clean blend (RAT, TubeScreamer, Bass Fuzz, etc). Then at rehearsal, I was able to experiment with different distortion settings to see what worked best with the guitars. This would not be possible with the Fractal products.
With regards to Fractal having better sound quality, I think that comes down to individual preference. Having never played a Fractal product, I don't feel comfortable commenting on the sound quality (for bass). From what I've heard, the Fractal is at the same level or slightly better than the Helix products. However, with the Fractal, you're sound is basically limited to the thunderous tube head amps. If you wanted a Pearce or GK like sound, you'd have to spend a lot of time trying to come up with a patch to emulate it. When it comes to guitar, I think the Fractal definitely has an edge over the Helix (in terms of sound quality and amp selection), so if you play a lot of guitar that's something to consider.
If Fractal would actually start caring about bassists, I would love to get a Fractal product and do a proper comparison between it and the Helix. The majority of my dislike for Fractal is not because of the amp models or sound quality, but because of their attitude towards bass. Its hard to justify spending 1-3k on a piece of gear (depending on AX8 to Axe FX III + foot controller) when you know their entire R&D budget is going to go into guitars amps/effects and you might see a token update in 3-4 years, especially when a competitor provides excellent updates for bass. If all you do is play a straight "bass -> SVT model -> cab -> out to board signal", I think the Fractal would be a great choice, and might even sound better than the Helix with the same signal chain. But if you like using lots of effects, or like having variety in the amp models, I think the Helix definitely comes out on top.
