First, it’s important to point out that the OP asked for opinions, and that the ethernet cable believers do not have monopoly here. Many post in a civil manner and keep things respectful, but there are a a few that do not -- you know who you are -- and just so you know you don’t come off as credible by insulting other people or chasing them out.
Now, on to the topic at hand: I’ve had many, many different ethernet cables. Probably hundreds, albeit none purchased with the idea of changing the sound in mind. Doesn’t mean I wouldn’t notice a change if it occurred.
I agree that really cheap cables should be avoided, because the ends are crappy and their ability to hold a good connection degrades terribly over time and the physical ends degrade.
You may also want to stay away from Cat7 if you are concerned about any form of EMF (highly theoretical) traveling down because the shielded ends can defeat the otherwise inherent galvanic isolation of ethernet.
So, buy well constructed cables within spec. Some "audiophile cables" are deliberately out of spec so beware.
If you review the myriads of discussions out there on the point of ethernet cables for audio (not just here - Roon’s forum, AudiophileStyle, plenty others) you will notice that those with science, engineering, and networking credentials come vastly down on the side that there is no way that the composition of the ethernet cable will impact sound quality except by being faulty and causing dropouts. No deeper soundstage, no crisper highs.
Ethernet is packet based with robust error correction that moves well faster than necessary to keep the streamer buffers full. There is no meaningful possibility of data errors affecting sound quality.
Noise on the line is a separate issue, but the material composition of the cables won’t change that. Isolation does. Ethernet already provides that if you don’t deliberately defeat it. But if you’re really double concerned, you can eliminate that issue with fiber optic network cabling (requires an adapter at each end) which is quite a bit cheaper than many of the more exotic ethernet cables...plus with fiber you know you’ve nailed it first time and there’s no swapping out cables to see where the soundstage is better. That said I believe fiber to be completely unnecessary but in science and engineering it is at least an undeniably supported solution to this theoretical concern.
Not here to argue. We do not need to start a debate. I just believe it is important to have balance in these discussions. Ethernet cable believers are eager to chime in and recruit...I just want people to think logically for themselves and understand the tech before they spend their $$$.