User blog comment:Vanguard13/Pick Your Poison (Ammo, that is)/@comment-3325589-20120811182737

ME2: Warp Ammo. While its bonuses aren't spectacular, it helps against the broadest spectrum of enemies. It's also the one ammo type with a bonus to damage against barriers, which many of the hardest enemies in the game have (Collectors, Praetorians, asari and krogan uniques). Least favorite is Shredder Ammo; I play on harder difficulties where everything outside the tutorial level has defenses that Shredder can't touch. Plus a lot of boss enemies are mechs with armor instead of health (Geth Colossus, Human Reaper, Praetorians again), so Shredder is never useful against them. Cryo's a little better, because it at least locks enemies down, but it's still nearly useless on hardcore and insanity.

ME3: Toss-up between Warp and Disruptor. Warp Ammo is now very effective against armor, and has the best damage bonus against health, making it very useful against everything but shields. For those there's Disruptor Ammo, which also has a pretty useful stun effect. My least favorite is harder to say; unlike in ME2, where some ammo types were obviously terrible (at least on higher difficulties), they all have their uses. I'd say Cryo, not because I think it's actually bad, but because my favored class is infiltrator, meaning I focus on killing enemies quickly rather than debuffing them, and Cryo is the worst for that.