How well do different kinds of birth control work?

Very well. Depends are which ones you are talking about. If taken correctly most forms work well. The highest failure rates come from the withdrawl method (terrible method in my opinion), condome (even though they should be used to prevent stds) foam, local methods. But if you combine the condom with foam or film the effectiveness goes way up. Pills, pagtch, ring should work well is used correctly.