Most lightweight browsers are based on WebKit (e.g. qutebrowser, dwb, luakit, ...), some are based on WebKit2 (e.g. lariza or GNOME's "Web"). Both engines work okay for most web sites. WebKit2 appears to be much more stable, but it's slower and not really suitable for old/slow computers. Sadly, there are enough web sites out there that crash both engines or make them crawl to a halt. That's why I use Firefox at work -- I can't afford a crash.

Yes, it's almost always WebKit's fault when one of those lightweight browsers crashes. I don't blame the WebKit guys, though. Have you tried writing or porting a web rendering engine? I have not, but I do know that this is an insanely complex task.

(Due to WebKit2's design, lariza does not fully crash. Instead, the crashing tab reloads. Still annoying.)

QtWebEngine is rather new: https://wiki.qt.io/QtWebEngine. It uses Chromium as a backend. Some quick tests of mine showed promising results, but a full port of lariza to QtWebEngine is still on my TODO list. Last time I checked, QtWebEngine was not yet complete. And as far as I know, there is no browser (yet) which uses QtWebEngine.

tl;dr: At the moment, it's Firefox. Let's wait for some QtWebEngine browser.