Certainly, "Best" is dependent on what you use the computer for and on your opinion.

As to "latest", Windows 10 is the latest version of Windows and is working for most and although there are problems, just like previous versions of Windows, we find it works fine for us. If you're into Mac OS X, then I believe it's "OS X 10.6 Snow Leopard." And for Phones and such, there are others. Unfortunately, you didn't tell us what you're going to use the OS for.

And "latest" certainly won't be here in this "Legacy" forum?

Hope this helps.