What are the important differences between the RSF and army in Sudan?

In the little western media I've seen covering Sudan, the general impression I get is that the RSF is worse in terms of human rights abuses, but that initially the army and RSF initiated a coup together.

Is it just two power hungry factions falling out, or are there deeper ideological differences? For example I came across a reddit comment saying RSF are atheist ultra-nationalists, which may be true or false, but I haven't come across much info characterizing the two sides motivations at all. I'm interested to know more, I don't feel like the coverage I've seen has been in depth.