I think the meaning of "wow" all depends on the context of the conversation really. It can be used to express shock, surprise, happiness, congratulating. So as you can see usually positive emotions. I guess you could say something like "Wow that's really bad," but for me "wow" on it's own would usually be for a positive situation. Regarding a sound for when you are disgusted, could be an "urgh!" For upset it could be an "oh" (said in quite a soft volume). Finally for shocked maybe an "huh", said in a sharp rising tone. Regarding the other pause type words, I couldn't say if one is used more than the other, I think it's all down to individual preference! "Ummm" and "ermmm" are usually used when you're not sure of something and "uh huh" is used when showing agreement or acknowledgement.

Another way to express disgust is "ewww".