Ask HN: What is the current state of browser engines?

I am no web developer, far from it, but I find the whole ecosystem interesting. Stemming from the debate around trying to get Apple to allow third party browsers on their mobile platforms, I was wondering about the current state of engine toolkits. How do they compare, what are their pros/cons/quirks, which do you prefer working with, etc?

- Chrome: Blink + v8

- Firefox: Gecko + SpiderMonkey

- Safari: WebKit + JavaScriptCore