Stable Diffusion seems to be the most popular AI image generator for porn, but the latest version, SD3, has been widely reported as terrible at humans in general because it was not trained on NSFW images.

I have not used SD, but Marcus's results are quite impressive.

Bing is the most popular AI image generator over-all, but it often produces images with that characteristic AI look that is a dead giveaway. Whether that is good or bad is a matter of personal preference.

Midjourney is highly regarded for its artistic output, but it is expensive and has restrictive licensing terms.

I have used only Ideogram, which I think is capable of producing good results, but it can be very frustrating and does not do NSFW images.