You know people who use WinRAR?
Depending on the platform I'm using I have some code in bash, Powershell and C# to deal with this. Non coders must have a hard time !
From my observation, most downloads are rar format (95% at a guess), but it doesn't really matter if it's rar or 7z as the differences in resource usage are negligible.
The good news is that most archives support free extraction of both formats.