I'm not sure I understand what you are asking. Both options are valid and one isn't better than the other fundamentally. Depending on your business needs, one might be better. For example, if you are going to display the ID, it might make sense for it to be something you generate that looks nice. If you care more about uniqueness and minimal effort, letting the system do it should be fine. But maybe I misunderstood what you need help with, in which case, a bit more context might be helpful.