Dogs really are VS Dogs are really [closed]

In the second sentence more emphasis is put on "really." If you place the adverb there, you really want to stress what dogs are. A few more examples like that:

People really should do something about the climate change! (this sounds a bit more urgent than "People should really do something... .")

I was doubting him, but after he helped me in that situation, I know that he really is my friend. (here, by placing "really" before "is," you contrast how you used to feel about the person and how you feel about him now).

We usually place the adverb after the verb to be. So, "dogs are really our best friends" is certainly correct, but it doesn't show the emotion that "...really are..." does. "Really" expresses the degree though. But still, "...really are..." is even stronger.