User blog comment:Vanguard13/Pick Your Poison (Ammo, that is)/@comment-1388547-20120810211801

ME1: Tungsten for synthetics, polonium for organics (extra poison damage is kind of nice, and it stops krogan from regenerating). I also save some cryo rounds for Saren, since they can still do damage to his health through his shields, or while he's doing his insanely powerful shield boost thing in the first part of the fight.

ME2: Disruptor Ammo vs. shielded mercs, Incendiary vs. Blood Pack. I usually took Warp Ammo as a bonus power so I'd have something that's good against all enemy types (particularly Collectors).

ME3: Still undecided as to my favorite. I ended up preferring Armor-Piercing to Warp for my Infiltrator; shields/barriers are generally less prevalent and squadmate power recharge is faster than in ME2, so Disruptor and Warp Ammo aren't as important. Besides my Infiltrator, I've mostly been playing biotic characters in SP, so I haven't actually been firing my gun all that much. :-)