Hi. I'm seriously considering using Arc as my main browser. It's based on Chrome, though, so it's heavily google-fied. But! It's similar to Vivaldi, in the sense it's unique. The tab tree is on the left and you have a split screen option in the task bar area. You can add chrome extensions also, which is great. It's semi-aimed at power users. I haven't discovered all features yet, so far I'm pretty impressed. It updates almost daily/regularly. I'm definitely gonna put it in my roster of main browsers.
Problem with chrome extensions is Google - they're deliberately limiting what Chrome extensions can do as of June, to enable Googles ad business and privacy invasion. If you value privacy and freedom then you're better avoiding the entire Blink/Chromium ecosystem if you can.
That only really leaves Gecko/Firefox related projects or Webkit related projects.
Also I'm not sure a browser that updates daily is a good thing - not a very realistic way to QA software for end uaers? Works for nightly builds on a project or beta software at a push (but daily is a bit much) but hard to ensure an update doesn't break something for end users if you're updating every day? Fine as a curio or of interested in it as a side project, but may not be fun to rely on as a daily driver?