My favorite ayah (currently) is
يَـٰبُنَىَّ أَقِمِ ٱلصَّلَوٰةَ وَأْمُرْ بِٱلْمَعْرُوفِ وَٱنْهَ عَنِ ٱلْمُنكَرِ وَٱصْبِرْ عَلَىٰ مَآ أَصَابَكَ ۖ إِنَّ ذَٰلِكَ مِنْ عَزْمِ ٱلْأُمُورِ ١٧
"O my son, establish prayer, enjoin what is right, forbid what is wrong, and be patient over what befalls you. Indeed, [all] that is of the matters [requiring] resolve." (31:17)
What's your favorite ayah?