You have a ton of options for different ad blockers on iOS, but if you're really only annoyed by comments sections (which, depending on the system they're using, can take up a lot of bandwidth), Shut Up blocks out just the comments and nothing else.
Once you enable Shut Up for Safari, you'll stop seeing comments sections for most popular web sites. The app uses shutup.css, so if you've used that on your desktop computer, you'll know what to expect. The nice thing about Shut Up is that you can easily set up a favourites list of sites where comments are always on by default, so you're only blocking the places where you really don't care.
Shut Up (Free) [iTunes App Store]