Are you gigging? If not then I would just stick with Bias. However if you need a hardware unit for gigging then continue reading... Here's my background: I've used Helix on the road for >3 years. Picked up a III and FM3 a couple months ago to learn something new while on COVID lockdown.
- Recorded sounds: Through the same IRs I don't think there is as big a difference in recorded tones of well-dialed-in equivalent amps as some claim. Helix's biggest weakness is the default settings on the amps and cabs, which are usually laughably bad. Through the same IRs, the Fractal amps are easier to get usable tones because they sound like the real amps should, whereas the HX stuff takes more work, but like I said, if you can dial them in they can sound quite similar on a recording. I do think the Fractal stuff has the edge though. It's most noticeable on the high end, where the Fractal is a little smoother and more natural sounding.
- Feel: I think the Fractal units have a more realistic or "3D" feel to them. It's hard to explain but when playing the Fractal it really feels like I am playing an amp mic'd up somewhere out there, whereas the HX stuff just feels a little flat by comparison. Compared to the HX models through the same IRs, the Fractal amps clean up with the volume knob better and break up more accurately when you dig in. This is something that would not really come through in a blind A/B listening test, especially with gained-up-internet-metal tones that seem to dominate the modeling world. But if you play other genres this is pretty important.
- Wet effects into the front: I rarely see this mentioned but in this area Fractal is the clear winner. A lot of people who use modeling run their wet effects after the amp+cab but if you want to recreate the "pedals into the front of a cleanish amp" thing then Fractal is the better choice.
Once COVID is over and we're touring again I will be transitioning to the III for my main rig. For me the most important variables are: 1) reliability/ruggedness, 2) consistency (so the IEM mixes are the same whether it's a short festival changeover or a full headline show), 3) size / ability to check on an airplane, and 4) tone. Helix and Fractal are pretty much tied on 1-3 and Fractal has the edge on 4. If I were gigging locally on a tight budget I would probably just use the pod go as an all-in-one rig.
For bass the Stomp is a better choice than the FM3 because it has the ability to run two amps in parallel with a crossover split.