For me, it was a close top 2 between the Scattershot and the Binary rifle. Each weapon in my opinion have their own bit of enjoyment in the games. Only reason the Binary rifle wasn't a clear winner is because of how it preforms in Halo 5. If they had kept it relatively the same from 4 to 5, it would've been great to me. noting was gratifying in halo 4 to quickscope someone from halfway across Ragnarok. However, the Scattershot on the other hand got a massive buff from 4 to 5, making it a very satisfying shotgun to use. the oneshot potential and the crispy animation of your enemy flickering away into an orange dust right in front of you looks and sounds amazing.
all in all, Halo 4: Binary rifle > Scattershot Halo 5: Binary rifle < Scattershot