I used to use both of these popular browsers, and now I'm all-in on Brave. Chrome is fast but has well-documented privacy issues. But even running various tracker blockers and a Pi-Hole, Chrome wasn't nearly as fast as Brave (without additional blockers or the Pi-Hole).
I like to support Mozilla/Firefox, and Firefox has been my daily driver for most of the last two decades. But it just isn't as fast as Chrome (let alone Brave). It has better privacy than Chrome, and the inimitable Tree Style Tabs, but it takes noticeably longer to open new tabs and load pages.
I moved over to Brave once they started supporting Chrome extensions. I have found that my MBP's fan kicks on much less often than before on Chrome/Firefox, and the battery lasts longer as well. While I miss the TST that I enjoyed on FF, I'm getting by with Sidewise. The inconvenience of having the tabs loaded in a separate window is massively outweighed by the speed/privacy benefits of Brave.
As for the ethics of ad-replacement, this is a bigger question. If the baseline were "everyone has ads everywhere", this could be seen as an unethical alternative. But the baseline is "many people (and presumably nearly everyone who is savvy enough to install Brave) use adblockers". So it's not like they're going from seeing ads to not seeing ads. They're going from blocking them with one system to blocking and replacing them with another system. And they can send the revenue from the replacement ads to the websites they spend time on.