I don't know about other usages, but energy consumption while using YouTube is important to me (usually have something playing while I work) so I just did a quick measurement.

Safari 13.0.2 versus Firefox 70.0 versus Chrome 77.0

Playing the same YouTube video at the same quality (1080p) and watching Energy Impact in Activity Monitor while the video played, I saw averages of: Safari used 20, Firefox used 45, Chrome used 45.

So on that task at least Safari is still king, but Firefox is on par with Chrome.