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When an inexperienced student sees $a=b=c$, I'd assume that both $a=b$ and $b=c$ are clear but the transitivity that yields $a=c$ might not be obvious. That's why I'd focus on this hidden equality when reading it out loud, by not just reading the equation (your first option), but rather saying "a, b, and c are all equal" or "a, b, and c are the same number" ...
I think how you read (and write) them depends on how they are being used. $$x^4 - y^4 = (x^2- y^2)(x^2 + y^2) = (x - y )(x+y)(x^2 + y^2)$$ is fine but pedagogically \begin{align} x^4 - y^4 &= (x^2- y^2)(x^2 + y^2)\\ &= (x - y )(x+y)(x^2 + y^2) \end{align} is better. More important is dealing with this common misuse of chained equals ...