What army has the most erotic potential?

Eldar are probably at the top. They're the one where everybody is supposed to be pretty and have muscular, lithe bodies. There's lots of women in the model range too, so it's not just lore.

Sisters are up there, just for all the reasons.

Mechanicus are definitely a dark horse tho. Body modification, brainwashing, dronification, it's really fertile territory for hardcore perverts