There is no good or bad exercise. Rather it is the right exercise for the right person, at the right time and performed the right way.
Exercise is a stress and every session has a cost. Balance your training with the right amount and quality of recovery to ensure the effects are positive.
Fitness is made up of many factors. The fitness to run a marathon is very different from that required to sprint 100m, throw a discus compete as a bodybuilder. The type of training that you should do depends on your particular goals.
Like the saying goes if you fail to plan you are planning to fail. Get clear about your goals and set objectives for your training.

Foundations of Health

Remember, optimal health and vitality begins with these six foundational principles;

Thoughts. Healthy thoughts create healthy bodies
Breathing. Focusing your attention on deep healthy breathing reduces stress
Hydration. For optimal health drink .033 L of water for every kg of your bodyweight daily
Nutrition. Eat high quality organic food that is right for your biochemical individuality
Sleep. Getting to bed before 10.30pm every night will promote optimal health
Exercise and movement. Exercise regularly and include energy building exercises for vitality