Your operating system doesn't matter as much, go with what you think is more usable for you.
A paranoid would say that it matters if the OS is open-source, which is true only for the latter. So, if you're feeling extremely nervous of which option is better, then I'd recommend you Tails. It sounds more honest to allow everyone look into the code.
Tails Linux OS is obviously better for privacy than windows and you won't have nightmare tracking and spying like with win os.
How could they spy on you if it's air gapped? You're supposed to never connect the internet.
Yes, and someone more paranoid than your paranoid would point you to Heads rather than Tails.
As for the air gap, remember how Iran got their expensive centrifuges damaged by malware some years ago, those were air gapped too... Their mistake was running SCADA using Windows and of course someone brought an usb stick one day...
If you care enough about using an air gap, get rid of Windows. It doesn't need to be Tails, i see no point if the machine is not connected anyway; any distro would work.