Supplication (Dua) is the best worship act

The Fifth Imam (a) was asked: What is better: excess of reciting the Holy Quran or more supplications? He replied: Supplication; have you not heard the words of the Most High: “Say: My Lord would not care for you were it not for your prayer”? This is also concluded from the Quranic verse: “…surely those who are too proud for My service shall soon enter hell abased.” Therefore supplication in itself is a worship act; rather it is the best of worship acts and the most beloved of deeds to Allah.
(Saheefa-e-Baaqiriyyah)