The best treatment for ED is the one that is best for you. Viagra (sildenafil) and Cialis (tadalafil) are the most commonly prescribed and are equally safe and effective. In most cases, lifestyle and cost will help you decide between them. Viagra (Cenforce 200), Cialis (Vidalista 20) and Levitra (vardenafil) belong to a class of drugs known as PDE5-inhibitors. To understand how they work, we’ll need a quick 101 on erections: For a man to get an erection, a chemical called nitric oxide sends a message to the tissues of the **bleep**, which relax and fill with blood.