Generally if it stores user input it needs to support Unicode. That said UTF-8 is probably a way better choice than UTF-16/UCS-2
UTF-8 is a relatively new thing in MSSQL and had lots of issues initially, I agree it's better and should have been implemented in the product long ago.
I have avoided it and have not followed if the issues are fully resolved, I would hope they are.
The one place UTF-16 massively wins is text that would be two bytes as UTF-16, but three bytes as UTF-8. That's mainly Chinese, Japanese, Korean, etc...