So I just compared them myself for my typical work and media playback (Youtube & Twitch), just anecdotal and totally unscientific though, ranked by MacOs's Energy Impact with the best being 100%.
All with the same extensions (if available, for Safari I used adguard instead of ublock origin).
Safari Technlogy Preview: 100%
Brave Beta: 110%
Orion: 300%
Firefox: 1200% :(
While Safari also used slightly less memory, Brave is the best compromise for me for now. (e2ee sync, chrome extensions and with their crypto shenanigans disabled.)
But again, not scientific at all and of course might differ for people depending on the extensions they use and their browsing behavior.