We use a dedicated HTML to PDF engine (such as PrinceXML) rather than building on top of a browser. Main issue with browser-backed implementations is that PDFs are often of subpar quality. However, the main good thing is you can rely on the latest CSS features.

In the end, what was the main decisive factor is the support for the PrintCSS and PagedMedia specifications, which have been completely discarded by major vendors and only implemented by specific engines.