Belief in, and fear of Satan probably culminated in the late middle-ages; Luther's way of recounting his conversations with the devil already show a certain (literary, humoristic) distantiation from it. It is certainly very low among Catholics (at least in traditionally Catholic countries) now.
In a sense JWs are closer to a medieval mindset with the huge difference that it is a subculture, and as a result their mind (like that of all "literalist" or "fundamentalist" believers, more or less) is a mix of two very different worlds. The supernatural understanding is switched off most of the time but it is lurking and can pop up anytime, as soon as there is a problem with the ordinary, "rational" functioning.
Now do JWs fear Satan more than Jehovah? I suppose it depends, but looking back to the fears I remember from my JW period, I personally wouldn't construe it that way. I think what I really feared was rejection, separation from God rather than punishment. And in its essence this fear was very similar to that of "hell" (as I recall from early Catholic childhood). "Satan" and "demons" on the one hand, "Armaggedon" on the other hand, were just names and figures that would fill that void -- but inasmuch as they were "something", they were actually less dreadful than the void itself. And at this point it mixes with very personal, non-religious emotions and fears from infancy. Fear of the dark. Nightmares of the "underworld" and the animal souls there. The unbearable pain of hearing my father say to me: "I don't love you anymore" and me crying "Love me, please." When you search for the roots of fear you may get very far away from theological generalities -- although they can be expressed in theological generalities.