きれい has a lot of meanings. Beautiful, clean, clear, neat, etc.
きれい can be used at men as well when you say somebody is handsome or good looking.
Like きれいなお顔の男. A boy with a beautiful face.
すてき is mostly used by women but not limited to women. It means lovely, superb, great, fantastic, cool.
すてきな人. A great person. A cool person.