Michael's hormonally charged observation belongs rightfully here:
In terms of sexiness, they were about on the same level for me, with Nena possibly having a very slight edge. There was no contest going on, but I guess that's just the way my brain was perceiving things. There was a lot to process for hormone-driven males.
And if I may add: Both Kim and Nena were nothing less than chastely in comparison to most dance acts today where a strip club atmosphere is never far away. They flaunted an uncontrived,
natural*** rock/pop-chick female sexuality, you could enjoy their vids and live performances without any porn-guilt creeping in. Sure they dressed and were made up to look the part, but again it was all within reason (yet attractive enough to dim your own). Vocally, neither of them was Aretha Franklin or Karen Carpenter, but they had nicely recognizable voices with Kim probably being technically better and Nena making up for it with charm.
***In case of Nena, for American eyes probably
slightly disconcertingly so, you guys know how weird you are: