In my opinion, you should exercise daily. But this mainly depends on the type of exercise you do and how long it takes your body to recover.

When running or doing most cardiovascular activities, it's possible to safely do them every day, provided you're in good physical condition. In fact, it's generally recommended you do this at least three times a week for a minimum of 20 minutes each time. Someone training for a marathon or road race might run six days a week and take only one day off (like Sunday). The same is true for most high school and college track teams.

Weight training and other related activities typically require more recovery time and more planning. When weight training, it is generally recommended you workout each muscle group at least once a week. Serious athletes will still go to the gym almost daily, but they typically workout only one or two body parts at a time, which allows other muscle groups to recover. For example, they might go the gym five days a week, but will generally not exercise the same major muscle group more than twice.

Some muscle groups take longer to recover than others. This largely depends on the type of exercise and body part. For example some areas, such as your abdomen, can be exercised several times a week and some exercises (like pushups) can even be done several times a day. However most people would wait a few days between chest workouts involving free weights (like bench press).