QC supposedly does a fair amount of filtering to their models which are not found in the real amps. I haven’t verified that myself, but it would explain someone finding it much easier to get good results quickly with.
I've read this before. I think it is just internet forumer waffle nonsense. I don't think it has any basis in reality.
For my money, having Axe3, Helix, and QC in my posession currently:
Helix Pros:
Helix has quite a lot of amps, and covers the essentials. There are also a few like the Revv models that are a little unusual, and sound great!
Tons of effects, which are high quality. I think Line6 adding all of their legacy effects to Helix was a master stroke of product spec design. It really makes Helix massively attractive to me.
Cosmos Echo, Transistor Tape, Adriatic Delay. Those are seriously good delays!
As a package, everything just sounds GOOD. There aren't many outright terrible sounds in there, truly.
Considering the price differential versus the Axe FX III, the Helix sound quality (conversion, signal to noise ratio, etc) is surprisingly top tier. If you're familiar with older units that Line6 did like the HD500 series, then you need to know that the Helix is leagues and leagues above that era.
Helix Native - for me, Helix Native is an essential bit of kit. I love the transferability between the software and hardware too!
Helix Cons:
Despite what I said about the effects, I'm not a fan of the reverbs. There isn't really a reverb that competes with something like the MXR M300 Reverb, the Meris MercuryX, or the Fractal Cumulonimbus algorithm; those long washy but smooth pad sounds are incredibly difficult to find on Helix.
I really do not like the tuner. I used it as my main tuner for years, because Helix was my main effects platform for years, and actually I had sort of forgotten how good your bog standard Polytune is in comparison. The Helix tuner is just not good, which is a shame.
QC Pros:
Running multiple captures in a single preset and flipping between them using scenes is GREAT.
The stock amps are all actually really decent. You don't have to use multiple models, you can just load a single block, and you can switch between the clean and crunch channels directly within it. Feels way more amp-like as a tweaking experience than the others do.
The tuner is decent. Not perfect, but decent. Better than Helix.
The touchscreen is useful. Not a gamechanger by any means, but it is useful. My experience with my current unit is quite different to the first one I had. So I've changed my tune here a bit.
The looper is fantastic! At its core... it is the same looping experience you'd expect from a DL4, or a Flashback X4, or any of those four button loopers. But it has quite a few cool additional features that make it stand out. I love being able to duplicate a loop 4 times and then track something else over the top that is longer. Very useful songwriting tool.
QC Cons:
Slow development cycle, and updates are always a bit lacklustre in my opinion.
The unit itself is small, which is both a good thing and a bad thing. The pooswitches are too close together, and it is very easy to mishit them.
The delays are bang average.
The reverbs are bang average.
The modulation effects are bang average.
The effects loops are not unity gain. There's no documentation about how to get a true unity gain signal path.
The unit is noiser. A lot noisier than Helix and Axe3. Turn off all noise gates and setup a typical high-gain recto style sound... and play a chord.. listen to the noise floor. It is not so good.
At the same time, the unit is quiet. The output of the unit always needs to be cranked, and then whatever your poweramp is, that ends up being louder than it would with the other units too - thus.... increased noise.
All in all, I don't think their hardware design is actually that impressive.
Between the two, for me it is very clear that Helix is the more well thought out and "planned for" unit - Line6 have a proper development schedule they're following, they have engineered a unit that will stand the test of time. Released in 2015, it has almost been 10 years. You don't see mass reports of hardware problems, of people being unable to get their unit repaired when they need to, power supplies randomly dying, etc....
Quad Cortex was released in 2021, and even now in 2024 I have very little faith that any of us will be using a QC in 2031. You read about hardware problems and weird little things that can't be reproduced all of the fuggin' time. Their discord is full of it. Their forum is full of it. And I think generally speaking, there is an air of frustration and unhappiness around the QC because of how they launched it, and how little they've developed it since release.
I like the QC, but I don't ever see me making it the cornerstone of my rig like I did with Helix. I gigged Helix from early 2016 through to 2022, and I went through a couple of units and always came back to it because as a platform it did everything I needed it to, and it was easy to use and sounded great.
These days, since TNBD ended, I'm less tied to it as a platform. But I still have the unit for now, and I think at this point I might go through to the studio and play with it for a bit!