Comprehensive and fast ad blocking. I took a chance on this because the iOS version is so good.
On Safari I used to use Ghostery, and then settled on uBlock for Safari and Chrome. Now I use 1Blocker in Safari, which seems a bit faster in operation than uBlock.
Tweaking blocking to let in some things can be a bit more fiddly than with other options, but overall I'm very happy with 1Blocker. (FYI I still use uBlock on Chrome, and Chrome is my primary browser.)