About a month ago, the Freakonomics radio show asked the question "What's The 'Best' Exercise?" in their weekly episode. This is a tough question, because there are many criteria you could use to assess this question. Does "Best" mean the one that works the largest variety of muscles? The one that we can do starting when we are young and continue until we are very old? Is it the one that provides the most cardiovascular benefit? Is it the one that provides optimal health benefit for the least input? Or is it the most enjoyable? As you can see, this is a hard question to answer.
In some ways, the answer to this question is: The "Best" form of exercise is the one that you will do regularly. Exercise is a habit, and hard work and persistence are more important than scientifically proven results. A "beach-ready" body that you have one summer when you are 24 is less valuable than the more moderately toned one you maintain for decades. Thus, the exercise that you find enjoyable enough to engage in regularly is the "Best" one. By far.
That said, there is some interesting research out there on the "value" of some forms of exercise as opposed to others, and the best way to quantify this is by using the MET as a unit of measure. MET stands for Metabolic Equivalent, and is a way to quantify the amount of energy burned by a given activity. 1 MET, for example, is roughly equivalent to sitting quietly, whereas walking at a slow pace has a MET value of 2, or twice that of sitting quietly. The higher the MET value, the greater the energy expenditure for a given activity.
But how do we use this information? What are various activities "worth"?
Well, Freakonomics would direct you to this document, produced by the CDC, which gives some examples of moderate and vigorous activity. You might find this helpful, or you may find it a bit difficult to navigate. I'd refer you instead to this website, which provides lists of all kinds of activities, grouped into categories such as Bicycling, Dancing, Home Repair, and Sports. Just about any activity you can think of has been measured and updated over the past 20 years.
While some of this information is what you already know - e.g. basketball requires more energy than billiards - it's still helpful for those who are considering picking up a sport for health benefits. But again we come back to the important question of what kind of exercise you will stick with. Running at a 10 minute/mile pace has a higher MET value than basketball, but the social reinforcement of a team sport is likely to keep you engaged over a long period of time. So take the information with a grain of salt. One form of exercise may burn more calories than another, but if you won't do it, is it worth investing in?
After all, what do you want to do to keep active?