I used to use Addblock Plus, but people on this forum put me onto uBlock origin and I have to say it's the best for browsers.
I used to have Admuncher for many years and found it pretty good for getting rid of system-wide adverts, and now its free, but I dont have it on my current system, as apps these days dont seem to suffer from ads as much (well apart from TuneIn radio & AVG products), and those that do I tend to fix by disabling the ad source in my hosts file.
I still have Peerblock, which isn't really an ad blocker, but prevents a lot of nasty intrusive pop-ups etc. Although its lists are fairly old and its not really being supported anymore it does stop a surprising amount of 'bad' stuff. I haven't tried Adguard, but it does sound useful.