When you say, "what other courses", do you mean other delivery methods for learning and getting certified in 6-Sigma, or do you mean alternatives to 6-Sigma?I'm presuming here that you mean the former.Certification in 6-Sigma, Prince-2, or any formal methodology, is worthwhile if you're using it on a regular basis or need to set yourself up as a content expert. Otherwise, you tend to forget how to use it properly.Doing a course can be useful if you want to pick up some ideas and methodologies to use elsewhere. It's a personal preference of course, but I find face-to-face training a lot more effective for learning than online courses. If you just need the piece of paper and know that you won't use any of it, then an online course from a reputable training company will do fine.