There are so many options, some good, some bad, and the answer will vary depending on the individual.
But if your goal is "Fat Loss" - meaning that you're carrying a few extra pounds right now and need to lose weight. Then there's one very popular type of cardio that I would definitely NOT recommend doing because it will actually hinder your progress in the long run.
I made a new YouTube video talking about this in detail sharing the PRO's and CON's of different forms of cardio...