Nextdns AI vs Quad9

I personally don't think security should be viewed that way. AI Driven Threat Detection does help, I found around 50+ sites that were blocked by it, around a dozen or so that no filters I had blocked so it's an additional layer of defense and it works but raw detection figures isn't everything.

Tere is no universal NextDNS test, the tests done through what filters the user decided to use. NextDNS gives that flexibility. It's your choice to be as secure or as free as you'd like.

There are filters that give you more protection from Malwaretisements and general malicious websites but some of them with the highest detection also have false positives, a great example would be 1HostPro, I haven't personally seen any other filter that blacklists websites as fast as they do but certain things that shouldn't be blocked are blocked, resulting in some sites not functioning properly.

From there, you can even have a near perfect DNS protection if you simply block everything and only whitelist the sites you use, even then the site that's trusted can be compromised.

What I'm trying to say is that, NextDNS is so flexible that the results change from person to person, you can increase or decrease the protection level by turning On/Off options like Newly Registered Domains, AI and general filters. It's up to you to decide. 

For what I mean by saying that security shouldn't be viewed by the basis of raw blockage / performance is.

Security should be unintrusive, if you have problems that security in my opinion is unnecessary and creates headaches. I don't personally use some filters that I know get the malicious sites faster, knowing that they tend to also block sites that brake functionality.

So instead of worrying about how much it can block, this is my opinion but look at the usability of the DNS, how speedy is it, what does it give you and how does it work. I'm not saying that Quad9 is intrusive or has false positives but what I'm trying to say is, Quad9 is setup for you, it only blocks Malicious sites and doesn't do anything else and it doesn't use third party filters so when you do a test on it, it's universal, it applies to everyone who uses it.

On NextDNS that's not the case, so set it up to your liking, based on what you prioritize and make it work your way.

As for a comparison, you can take the precautions aka using a VM that's setup properly a VPN to hide your IP for security reasons and comparing how you use NextDNS to how Quad9 does, then you end up with a result that you can compare. But even then it's not how NextDNS does but how your configuration deals with it. 

It's long and complicated, but I tried to explain why you can't exactly compare the two and that honestly raw blocking performance matters but it's not to an extent that it's make or brake.