Why you should prefer Cairo's png engine; visual proof.
In the past, copying plots from RStudio Plots pane to some document was a pain in the ass, having to deal with horrible graphics quality. I thought that problem was caused by my RStudio version, some issue with my pc or even by Windows. Turns out it's a mix, because RStudio's default PNG engine for Windows produces ugly plots.
Here's what I mean
ggsave(filename = "images/iris_default.png", plot = p,
height = 5, width = 7, units = "in", dpi = 500)
ggsave(filename = "images/iris_default.png", plot = q,
height = 5, width = 7, units = "in", dpi = 500, type = "cairo")