This thread is a little old but you don't have any replies, and although you have likely decided which option is best, I'll give my opinion anyway:
First of all, option one is out. You cannot say you have a strong work ethic and led by example - 'have' is in the present tense, while 'led' is in the past.
Option two is probably the best one to go with.
Option three says you have led by example. It doesn't seem to say that you have led by example all the time, which is what the interviewer wants to hear.
Option four is just as good as option two - either one of these two should be fine. But really, you shouldn't worry about it. Of course you need to know what to say during an interview, but its not necessary to know what you will say, word for word.