This would be a difficult decision because I have a Favorite weapon for the UNSC, The Covenant, and The Forerunners.
The UNSC: The Answer, Arrow or Time, and The Lawgiver
The Covenant: The Sword of the Faithful, Ravening Silver, Prophet's Bane, Tarturus' Gavel
The Forerunners: Dying Star, Didact's Signet
I am a Sangheili Leader btw but I will say that I don't play well with UNSC weapons in raids, training, and Recruitments