Help me decide Warbond

So I own alot of the Warbonds and I'm down to a remaining couple to decide which one I should work on next. Now I do not have Freedom's Flame, Chemical Agents, Control Group, Halo Crossover, or Masters of Ceremony. Currently I'm debating between Chemical Agents or the Halo Crossover.

Heres my reason for these two. For Chemical Agents, its the Gas Grenade which is one of the more useful grenades in the game. The Halo Crossover is for that shotgun which basically has the highest damage for a shotgun in the game.