As far as I know, uBO on Firefox is still a bit stronger than Brave Shields, but the gap is steadily closing.
DDG (at least on Mac) runs on WebKit, so it has all the issues of running WebKit, but if you care about the Chromium near monopoly, it's a way to get something that's not Chromium, probably has decently aggressive antitracking features, and has an engine web devs care about because of Safari.
Definitely do use uBlock Origin over any other variants or AdGuard variants.
DuckDuckGo is nice because of the bang support[1] and being able to quickly jump to another search engine, if DDG doesn't return adequate results. But your profile lists a duck.com account, so you're probably already aware.
If you keep copy of your firefox profiles folder, its not too much work to maintain. Most of the work is an upfront cost of setting up the initial profile.
There is also Librewolf, a Firefox fork which includes uBlock by default and has other security hardened features.
>And now we have DuckDuckGo entering the scene and I'm wondering how they all stack up.
IIRC, DDG is using the system webview for their browser, so the rendering may differ depending on the platform.
That leaves me with Firefox (or its less known forks: waterfox, librefox, palemoon).