Infiltrator ammo choices and tactics
So my game-play style basically down to using your tactical cloak to line up the perfect head-shot with your incredibly awesome Widow sniper rifle, with the ammo being depended to your target, disruptor for enemies with shields, cryo to set up an easy frosted kill for one of your squad mates like Garrus with his high impact shot. A good idea is warp ammo which you can pick up if Jack is loyal. It will tear biotic enemies and their defenses apart. I always pick it up as my bonus power because its awesome.
For your squad members depending on the type of enemies you will face its always good to try and balance it out. You will want a member with biotic powers (i usually go with Jack or Samara) and then depending on personal preference and the enemy forces either a true soldier like Grunt who can take a lot of punishment or a tech expert like Tali if you are gonna be facing a lot of synthetic enemies like Geth.
Last but not least it pays off to have at least one ammo type which benefits the entire squad and not only Shepard because you may find yourself picking squad mates that don't have an ammo power themselves. Hope you liked my tips and good gaming!