Honestly, it's what is more important to you.
Shredder Ammo leads into the Bullet Wizard build. Basically, you combine Suppression + Danger Zone + Mayhem + Holo Targeting + Shredder Ammo.
Suppression itself always succeeds. If your opponent provokes a reaction shot, then that shot is based on your hit chance, but it's not the important part.
Danger Zone applies Suppression to a group of targets close to each other, instead of just 1 target.
Mayhem deals 2 damage to all Suppressed targets.
Holo Targeting applies a +10 aim bonus to hit all Suppressed targets.
Shredder Ammo causes all Suppressed targets to take more damage.
Thus, the combination of perks allows you to AoE debuff groups of aliens with 100% chance of success. It's a great support build.
Flush and HEAT Ammo are more for dealing damage, which can also be really useful, but it depends on what you want to go for. Support or dealing damage.