When we use きれい as "beautiful", we often use it to women. Ex.　彼女はきれいだね。 　　 あの人、モデルみたいで、きれいだね。 　　 あの人の肌ってきれいだよね。 It is used to men, especially the man is super cool and his face looks like women like 女形（おんながた). Ex. 彼の顔はきれいだね。 　　 彼はきれいな顔をしているね。 彼の肌は（男なのに）きれいだね。 in my textbook きれい is also meant as 'clean', is it used in spoken japanese? Yes it is. Ex. わぁ〜、きれいなお部屋ですね。 　　　 きれいなお家ですね。 　　　部屋をきれいにしておいてね。 　　　 すてき、 do you use it for men, women or objects? 　Yes, you're right. We can use it for them. Women often use this phrase. Ex. 彼女はすてきな女性ですね。 　　彼って、すてきだね。 　　すてきな洋服ですね。 I hope the examples make you understood. Arrideverici (あってる？）

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.