What is the advantage of stock Android?

Forget about rooting for a moment. What is the advantage of stock Android over something like Nova? I heard that the pro version is pretty neat and resembles stock almost entirely in terms of pure aesthetics.

Besides faster updates on Nexus devices, is there any particular reason to buy (let's say) a Nexus 4 over a HTC One, if you can change Sense with another launcher...?

I've never owned an Android device so far, but I'm most definitely looking into buying one, and the One would be my first choice, so...

Thanks for your answers :)