Edge for me, since it has the single best implementation of vertical tabs on the market, with smooth expand on hover. Every time I try other browsers, I am immediately put off by how lacking in polish vertical tabs feel in comparison and go back.
As someone who loves vertical tabs, I was disappointed with Vivaldi's vertical tab behavior/implementation compared to Edge and Brave. I used Vivaldi full time for half a year before deciding to revert back to Edge for work and Brave for personal.
Of course you can customize with CSS and other types of things, but I'd ideally like my browser to just work well and be designed well.
Having said that, I miss some features from Vivaldi. However, I am much happier using vertical tabs in other browsers that have that feature.
