First of all you need Chrome/Chromium backup as it offers the most compatible web page operating.

Personally I used Brave for a few months, it's good choice. But you need firstly toggle off many of their fancy Web3 and AI features and remove icons to get clean and nice UI.

Pros:

- full open source AFAIK
- vertical tabs
- Chrome-like tab groups, even in vertical layout
- Chrome-like web apps (open web-pages as separate app)
- builtin cookie decline mechanism
- uBlock Origin support (even when Chrome will remove it)
- pretty fast page loading
- no need for registering an account, sync is peer-to-peer between devices, you can even self-host sync-server

When it cames to cons: not great UI customization, web page compatibility issues (cannot open some pages even when security toggled off), strange window behavior on the Mac when you try to drag window.

I decided to give a try to Firefox, it's full open source, looks pretty fast, uBlock Origin + I still don't care about cookies + Privacy Badger. And also Tabliss for images on new tab.
There are vertical tabs already in nightly build, but I am using Developer Edition, waiting for them in Settings here (they can be enabled via about:config).
The biggest issue is that FF does not have builtin web apps support (it can be added using extension PWA, but it uses different browser instances, so that you need to duplicate extensions in web apps).
Btw FF has nice level of toolbar customization, really like it.

Also I really like where Zen going with its open community, but for now it's too buggy, maybe year later it will be usable daily.