Rating swearwords or taboo words is not easy as long as the degree of "offence" may vary from person to person or from town to town. Even an exclamation like "Jesus!" may seem offensive to someone, believe it or not. Keep in mind that a word can be considered taboo in one culture but not in other, especially slang and swearwords.
As I don't want to reproduce such words here, I advise you to take a look upon Michael Swan's "Practical English Usage". He wrote a very daring chapter on this type of words and I think he kind of rated them.
Hope this helps!