Two of the biggest female rappers of all time, and two that definitely have a very similar (almost the same) style. Which one had more impact on music as a whole?
Kim easily. Literally no one can claim more impact in female rap than Kim. She opened a whole new lane that no one had ever dared enter before. Nicki lacks any real originality with the exception of her rapping style and she unfortunately became famous at a time when legends just aren't made anymore simply because of the nature of the internet and the short-attention span of the general public.
Scratch that, Nicki has had more impact overall. She's cemented herself as a lyricist to be taken seriously as opposed Kim who was passed around and has had most of her material ghostwitten.