1/ What's good for me is bad for the others. 2/ What's good for me is bad for everyone else. 3/ What's good for me is bad for everybody else. 3/ What's good for me is bad for the rest. They are all fine. Don't forget to capitalize the first letter of the first word of each sentence. Your first sentence is fine, but more common to say 'for all the others', rather than 'for the others'.