None of them are unattractive in terms of facial features and body. I'd give them all somewhere around a 5. I can see a situation where, if they weren't politicians, I could find Clegg and Miliband somewhat attractive, but Cameron - never.
I don't think of people in general in that way. 1) looks don't matter and 2) sex appeal can scarcely come over on any sort of screen e.g. I don't rate the chap who plays James Bond (forgotten his name), it's a mix of a lot of things which can only be experienced in person.