Hello, just have some thoughts. How often do you guys retrain your powers for specific missions on insanity? For the majority of the game, infiltrators have no real problems with disruptor ammo + incinerate, which basically covers most enemies, but the Reaper IFF is tough enough that squad cryo ammo is the best choice. The reason I bring this up is that I feel the ammo debate so far hasn't doesn't make it clear whether if it's under the condition of "if you had to choose one and keep it."
If I had to choose and keep one, it would be squad cryo ammo, because between cloak, the smg and the sniper rifle, I can pretty much handle handle anything, but the glaring weakness of the infiltrator is his lack of stopping power vs. charging enemies. Soldiers have concussive shot, while adepts, engineers, sentinels, and vanguards have throw/pull/singularity/shockwave/cryo blast at their disposal.
AP/disruptor/warp/shredder ammos make you kill faster, but the fact is the infiltrator doesn't need to kill fast under most circumstances. It's only when you are in tight spaces with flanking enemies that your choices will be either a) add so much more firepower that they will never touch you or

use cryo ammo to keep their distance. I've tested AP, warp, shredder ammo ad different squad members on the IFF mission to know that your SMG and pistol alone will not sustain enough damage to keep husks away from you. The armor on the husks are deceptively thin compared to their health, so the "if you see their red bars, they're already idea" idea completely gets thrown out the window in this case.
Cryo ammo is the infiltrator's ad the soldier's singularity. It stops charging enemies, and you deal double damage to them while they're frozen. Squad cryo ammo effectively stops the enemy from firing back, which means your squad takes less damage while they deal 2x damage and a chance to instant shatter. Even with the damage bonus from squad AP/incendiary/warp ammo, their weapons just don't do enough damage, and you rely on their powers to strip down defenses more than using their guns. So you might as well make your squad freeze them.