Which is better and more rewarding: performing the night vigil prayer (Qiyam al-Layl) at home with greater devotion and then going to the mosque, or performing it at the mosque before Fajr with the virtue of the first row and less devotion?

Performing supererogatory (nafila) prayers at home is more preferable and better than performing them in the mosque. If, in addition to that, you achieve more khushu' (devotion and humility) in your nafila prayer at home, then what is appropriate is that you perform as much of the night prayer (qiyam) as you wish in your home, because it is more conducive to sincerity (ikhlas), further removed from showing off (riya'), and closer to achieving khushu'. If the Fajr adhan is called, it is likewise preferable to pray the supererogatory prayer (sunnah) in your home, and then proceed to the mosque to catch the congregational prayer there. The bounty of Allah is vast, and a servant may attain through his intention what he might not attain through his action.