This is my first time through the game.  I'm playing as a sentinel, who doesn't have any ammo powers.  I unlocked shredder ammo (heavy version) for Sheppard and I usually run with Thane in my group and he's using the squad shredder ammo power.   My first thought was that my other teammates would get the shredder ammo from Thane while I'd be using my more powerful version to take down enemies faster.  Then I started thinking, what would happen if I changed my ammo power? 
 
 
If Thane is using his squad ammo power and I'm using heavy warp ammo, will his ability override mine and I'll be using shredder ammo?  What happens when we both use different evolutions of the same ammo power?

Activate Squad Ammo first, then activate personal ammo.

Comes down to what difficulty you play on.
I prefer Armor Piercing ammo on Insanity since theres alot more enemies that have it. Plus it increases damage of both health and armor. Incendiary is kind of bad-ass too since it can ignite your targets and make them...err, not shoot on you.

Warp Ammo.
 
 
I like flashbang a lot too, because sometimes you really need that arcing, area damage tool to flush guys out of cover.