What is the best/recommended Linux OS to run a stake pool?
On ARM hardware such as a Raspberry Pi 4B, I highly recommend this Alpine Linux setup written about by some members of the Armada Alliance of SPOs. It does a great job running Cardano static binaries while using very little power, CPU, and memory.
My pool (Adaberry Pi ) runs both Alpine and Ubuntu nodes very reliably on these little single-board computers.
I am a Windows expert since 3.0 (1988), and Linux/Unix almost as long. I am proficient in Windows 2019 and 10. Although there is a Windows solution for running a Cardano stake pool, I would not recommend it for many reasons. As far as Linux distros go, Ubuntu is an excellent one that I have worked with for almost 15 years, and I highly recommend it. It is backed by a successful commercial enterprise, but it is free to the community. As a Debian fork, it is relatively easy to use and well-supported. And, if that isn't enough to convince you, the shell scripts and installation documentation & courses are all using it as an example.
One thing you should know, is that Ubuntu labels their OS versions by year and 6-month release cycle. So for example, 18.04 was released in 2018 in April, while 18.10 was released in October. The April releases are more proven/solid, the October releases more experimental. Every other year is a Long-Term-Support release, or LTS, so 20.04 LTS has a longer-term support commitment from Canonical Software.
Also, for the Stake Pool I operate (PLL), I did some research and it is recommended to apply automatic OS updates, so we enabled that.
If you need more help, give us a shout on Telegram at https://t.me/tprevolution