They all do the same basic thing.
Chrome is by far the most popular browser. The DevTools work the same on all Chromium browsers (Google Chrome, The new MS Edge, Opera, Brave, etc.). Google has a free Google Chrome Developers channel on YouTube. It is really more for developers but has a lot of good current videos.
Firefox is excellent as well. If you want to develop with the latest CSS - CSS grid it is my first choice for that.
Safari is probably least used, so there is less training available. It works well, and the advantage here is the Safari Web inspector is built right into RapidWeaver preview and Simulator.
So I guess my answer is if you want to learn one for RW then Safari would work. If you want to get into hardcore development like JavaScript then Chrome or Firefox would be better.