Viagra is an oral medicine used for treating male impotence (e.g., erectile dysfunction). Viagra's advantages are a great safety track record and proven side effects. The effect of Viagra starts in 30 minutes to 1 hour and lasts for about 4 hours.

Cialis (Tadalafil) is an oral drug, used for treating male impotence, also known as erectile men's erectile dysfunction. Cialis' effect starts working in 30 minutes and lasts for about 48 hours, while Viagra effect lasts for about 4 hours. Cialis is to be taken with or without food.
Cialis is to be used for daily use, so you can be ready anytime.

Levitra (Vardenafil) is an oral therapy for the treatment of erectile dysfunction. Having the long-lasting effect of 4 hours, and the start time of 16 min, Levitra represents an uncontested advantage in comparison with Viagra.