Why Lord shiva is the most powerful GOD?
From Mahimna Strotra
महेशान्नापरो देवो महिम्नो नापरा स्तुतिः।
अघोरान्नापरो मन्त्रो नास्ति तत्त्वं गुरोः परम्॥३७॥
There is no god (devaḥ) that is higher (aparaḥ) than Mahesha --an epithet of Siva meaning "great Lord"-- , there is no hymn of praise (stutiḥ) which is higher than (this) Sivamahimnaḥ stotram . There is no Mantra --a sacred word-- which is higher than Aghora --an epithet of Shiva meaning "not terrific"-- (and) there is no principle (tattvam) that is superior to the Guru --in the sense of the fifth "kṛtya" or action of Śiva, which bestows divine Grace upon a limited being-- ||37||