I'm going through the process of converting ALL of my story covers to images that are copyright-free and not exploiting actual humans who may not have consented to the use of their likness. I am also deleting or hiding anything in my Media folders that might be questionable in these respects. I'm hearing about more companies getting litigious and even extorting settlements out of people, so better safe than sorry.
Nightcafe does decent SFW images, and although the process of getting free credits is a bit convoluted, it's not hard to pile up a decent stack of them. And while it's not AI, Creazilla also has a nice trove of stock copyright-free images that I use for quite a few things.
That said, I want to do NSFW images, including for story covers (because boobs), so this week I started experimenting with Perchance. As vampire_vixen found, it will generate something I can work with using relatively simple prompts and not too many attempts. If you just ask for nude bodies in various settings, it tends to do that fairly well, with reasonably realistic (but perhaps too pretty) bodies, including penises, breasts and (because I request it) pubic hair on women. It even gets the pubes right, usually, but occasionally generates a trans woman by throwing in a penis. Not that I mind.
Where Perchance seems to go haywire is if you ask for much physical action between the people in the image. It usually gets kissing right, and renders cocksucking acceptably about half the time, but anything more than that and you seem to end up with a tangle of phantom limbs, mutated genitalia and the usual malformed hands and fingers. Still, overall I'm happy with what I can get from a free tool.