I was asked to reply here in another thread. I represent AdGuard so take this with a grain of salt, but I promise I am trying to be objective here.
AdGuard is generally a more universal tool than uBlock Origin and any other extension, and certainly much more powerful than just a mere DNS server. It basically combines ad blocking, firewall, and a DNS filter.
The reason for that is that AdGuard works outside of the browser and controls everything, even things that the browser does not want the extensions to see. For instance, extensions are not allowed to operate on some web pages (Chrome WebStore, new tab, etc).
That said, to be fair, browser extensions have some advantages that are not easy to replicate on the outside since they have access to browser internals.
Anyways, compared to DNS AdGuard has full support for cosmetic filtering which is very important for ad blocking quality. Without it it won’t be possible to block ads on Youtube or Google search.