Qubes is currently the best option, but you also need to choose well which OSs you use inside of Qubes. I highly recommend a combination of Whonix, OpenBSD and Kicksecure.

OpenBSD

Install something basic with no network access. Anytime you need network, boot Tails and use that

Tails OS is only useful if all you want to do is buy few drugs or blowvwhistles on government or any other one off thing. But for daily driving tails OS is terrible.

The main selling point of tails is that it is amnesiac but I’m pretty sure most people will want to save some data on there device.

even though I’ve set priorities .onion but in reality most website I need are on clearnet with no onion mirror. I know this can open to network analysis attacks but I’m OK with it most of the time. (LEA Already knows I visit 7000 times a day). But back to the point all these clearnet site share data With each other and this could lead to cross contamination and sites able to build a proper profiles on you. Tails can’t do much here but with Qubes you can compartmentalize.

If you want to login to your bank account or some other site where you don’t want yo use Tor but still not share anything more than you want to Tails has no solution you will be forced to use a different less secure and private OS but again with Qubes you can create separate VM that will only connect to your bank directly.

Unpopular opinion but… First privacy and security is not the same, one relays on the other tho. So find your treat model when it comes to privacy. If its about security as you mentioems qubes is also great, yet needs a lot of knowledge. Your computer is only as secure as you made it and make it! Keep it up to date etc. For a normal user who don’t have the knowledge or used qubes or even Linux in the past it is probably a jump to high. Macos is secure, not very private. Consider all of this find out yout treat model find out what you use your computer for. Separate business and private accounts etc…

This is all down to your threat model and use case.

the most “secure” desktop would be an airgapped system, no connection to the internet, and no storage.

Qubes is great, but its not magic, you have to be clear about what you are protecting yourself against. If your using Qubes and someone steals your running laptop, your data is typically unencrypted, etc.

Qubes + always on vpn VM + tails disposable VM… is pretty good

I’m running Qubes now, its great, but its just a toolbox, you still have to build up your own usage model, how you want to separate identities and use cases and network stacks.

Darknet vendors mostly use Tails, as it makes it easy to wipe any tracks. The chance that they will be targeted with malware is low, they require privacy and anonymity over security.

Computer without any networking capabilities, no external drives, in a secure location. 99% secure (not immune to human error/social engineering).

Extra points if nobody but you knows about its existence.

If you’re asking about OS, Tails is a pretty popular one but I’m sure you’ll get better recommendations (sorry can’t actually help you!).