I would give QtWebEngine a try. It is replacing QtWebKit for a reason.
If you control the HTML that is getting rendered, then it probably doesn’t hurt to use QWebKit. Just make sure you test your pages beforehand.
QWebView uses WebKit as the backend.
http://doc.qt.io/qt-5/qwebview.html#details
QWebEngineView uses Chromium as the backend.
http://doc.qt.io/qt-5/qwebengineview.html#details
WebKit is what is used in Konqueror on Linux and Rekonq. Its not bad, but its not as robust across general (and often imperfect) web pages/html in my opinion.
Chromium is a much newer, faster and more robust engine.
I don’t know all the technical details specifically, but QWebEngine is a big step in the right direction. I’ve found this mostly from my own experimenting and empirical usage.
To give WebKit a decent try, look at this project and try a variety of pages:
http://qtweb.net/
https://github.com/magist3r/QtWeb
Here is some more info about QtWebEngine v QtWebKit
http://wiki.qt.io/QtWebEngine
http://en.wikipedia.org/wiki/WebKit
http://wiki.qt.io/QtWebKit