There isn't a "best" exercise to lose weight.
You don't need to exercise 7 days a week.
Exercise is great! Any exercise.
Including cardio (huffy puffy), plus strength, and flexibility work into your week is a great all-rounded exercise program.
But it doesn't matter what you do. It doesn't matter whether you prefer to cycle, run, walk, do a DVD at home, take up dance, join a football team, or anything else. Any exercise is good exercise!
And rest is a critical part of your exercise programme. You should have one day a week where, if you get any exercise at all, it's light and easy. You would probably also benefit from a week off every 8 weeks if you're pushing the intensity high every time.
Deb, in New Zealand