Which is greater in reward: inviting a Muslim to Fajr prayer, waiting for him, and accompanying him to the prayer, or praying in the first row for Fajr prayer?

Among the best acts of devotion and greatest acts of worship is guiding others to goodness. This includes helping a brother perform the Fajr prayer. If you wake him up and then leave before him, there is no blame upon you if you know that he will catch the prayer. However, if you know that he will be lazy and miss the prayer time, or miss the congregational prayer, then stay with him until you are sure he has woken up, or accompany him to the mosque, even if you miss the first row or the opening Takbir.