People love 'best of' lists. Whether it be when buying a car and picking up a copy of Consumer Reports or watching David Letterman's Top 10 List we love to have things ranked for us.And a common question coaches and trainers get from their clients is 'what is the best...' and you can fill in the blank for whatever it is someone might  ask when working with a fitness professional.For example, you might hear questions about what is the best stretch for this muscle group, or what is the best supplement I should take and another popular one is what is the best type of cardio I should be doing?Let's take a look at this last question, what is the best type of cardio I should be doing, and answer that one first.Step #1 - What is the Purpose?The first thing we need to know is why I are we choosing to do cardio in the first place? Is the end goal fitness or performance? Knowing the answer to this gives us a better idea of what the next step should be. Let me take a moment to explain.Actually, I'll back up another step here first as well. While the title and the body of this blog uses the term 'cardio' know that we mean energy system training (EST). When we say cardio, or cardiovascular, some people will understand this to mean aerobic training and not consider anaerobic types of training. However, fewer people will use the term energy system training, which includes aerobic and anaerobic training, so we are going with what most people are familiar with which is 'cardio'.Now to address the previous question are we looking to do some energy system training (EST) to get better for a sport or performance or are we looking it as a...