Everyone uses propaganda, so yes, always be critical of every source. But once you know what a sources biases are, there can still valuable information to be learned from them.
When sources contradict each other, as in the case of tankies vs. Lemmy, deciding which sources to trust can be complex and nuanced. Generally though, it comes down to sources who usually have a vested interest in the continuation of capitalism and often are outright fascists, versus sources who are communists and believe in equality and the betterment of all humanity.
In other words, qui bono?