Kaidan and Liara make my squad unstoppable!
Playing on a harder game difficulty makes this squad ideal because both squad members have powers that greatly affect both armor and barriers! And works if your Shep knows Reave.
The order of powers to use that I find highly effective against enemies with barriers and armor is the following: Get ride of the barrier - Liara uses stasis stops the enemy I their tracks and then equip her Warp Ammo. Kaidan uses over overload to zap away the barrier. Have your Shep and Kaidan take turns using Reave (Kaidan can still use Overload too) until the barrier is gone.
Once the barrier is gone, it's time to get rid of the armor. Liara can now use herWarp with does a bit of damage to armor. Kaidan's Cryo Blast and Reave are effective at this point. Your Vanguard's own Reave is effective. Equipping Cryo Ammo would be good too.
Now that your barrier and armor are gone, Liara and Kaidan can combine their Singularity and Reave for a very damaging effect. Your Vanguard can't hen do the ultimate Biotic Charge, heavy melee, and Nova combo for a nice ending!