Although exercise has been shown to be more important than dieting when it comes to one's overall health, one should also keep in mind to be realistic about one's exercise plans. It is all well and good to have grand ambitions, such as running the marathon or aspiring to be built like California's governor, but one must also keep in mind that for this to occur,that exercise would have to be one's #1 occupation. Everything else would have to play second fiddle, including one's spouse, children, work, school, and so on.
A far more realistic, liveable, and I think sane approach, is to do just enough exercise for your body that one's body needs. This involves no more than a few minutes of heavy weight lifting, stretching, and then finding some way to burn 300 calories per day doing aerobic exercise. As for which aerobic exercise to do, the more one enjoys it, the better. There is no point in choosing some form of exercise that one hates, because it simply will not last.
Personally, of all aerobic exercise, I think the best kind is a combination of walking, and occasional stair climbing. Swimming would be wonderful to, and is great for heavy people such as myself, as that is the one time when us heavy people can feel what it is like to be a normal person. But swimming does not offer one's legs the resistance it needs to get a full workout. Running/jogging is even worse, offering too much resistance, ultimately resulting in knee/lower back injuries. Walking offers just enough resistance, without the risk of injury, and is also the most natural, convenient form of exercise there is. No special equipment or fancy health clubs required. And when it comes to stair climbing, if you ever have to enter a building to some office or apartment off the ground floor, try to climb the stairs for 2 or 3 of those floors, taking the elevator for the rest of your climb upward. When taking the elevator down, do not use the stairs at all, as walking downstairs can cause some of the same kinds of injuries as jogging/running does.
Finally, when exercising, never, ever underestimate the importance of water. I know that water is the most boring thing one can eat or drink, but it also happens to be by far the most important thing one can eat or drink. Just think of how we all feel on Yom Kippur, how it is far easier to refrain from eating than it is from drinking water. And water is very inexpensive, plentiful, and has zero calories. One can almost never drink too much water.