I have found a PDF file, which looks horrible when rendered with poppler-glib or pdftocairo. It does render (mostly) fine in okular, so I guess it's either specific to poppler-glib or the cairo backend.
You can reproduce that bug with:
pdftocairo -png -r 90 -f 15 -l 20 exphy.pdf
or with Evince.
I am using archlinux with poppler 0.20.0 and cairo 1.12.2, but it also happens on a gentoo system with 0.18.4 and 1.10.2.
P.S.: I also experiences crashes when rendering this PDF file to a cairo PDFSurface, but only if I would use poppler_page_render() instead of render_for_printing().
Created attachment 62919 [details]
the problematic PDF (shortened. used to be 15MB in size)
The problem is with rendering bitmap fonts (e.g. TeX Type 3 fonts), or embedded black and white images, such as scanned images. Some 5 years ago there was a discussion of this on Ubuntu launchpad with a few examples that are still displayed without antialiasing in poppler/cairo even using poppler 0.26.5.