That's a tough question for me to answer. Each was so different than the other. Kes was very appealing to me, with her pixie haircut, sensual voice, and intelligence. Seven of Nine was the opposite - in your face lil Abner body in a catsuit to appeal to young (and old) fanboys. Kes was under-used; Seven over-used. They could have easily existed together on the show, since their characters and stories had little in common.
Right of the bat this is how i feel about it too. I think towards the end of Kes's run there was so much more to learn. We were really getting down to what her speices was all about. and i really loved the long hair. I never did like the pixie wig. looked to fake. As far as 7 I cant argue with a hot blond in a cat suit but i think she was over used too. I started calling Voyerger the 7 of 9 show.