I go back and forth on this one
Method one: Executioner
Ruger Super Warhawk, Smartlink, Ammo Skip, 'trodes. Couple Stick and Shock, couple Explosive, one tracker round. 2 speed loaders with Explosive and Stick and Shock.
As a mage you've got access to Increase Agility and Analyze Device, both have high utility outside of buffing your gun skill. You've also got access to Invisibility, Spirit Concealment powers, assorted mind control, and other horrible things, all of which have uses outside of gun battles.
If you weren't able to set up the ambush or buffs my own preference is Control Thoughts, "Don't Move" and a coup de grace on your next pass.
Method two: Mr. Tactical
Automatics skill, any weapon with FA, Open with AoE Debuff, pop (thermal) smoke, lay down suppression fire with Astral sight from good cover from inside your smoke. Let the team flank and mop up.
Method Three: Repeat Offenders style.
Mage with large defense tests (example Int tradition Mysad, maxed combat sense and a deflection prep running, you're around 20 dice without dodging. ) Open with AoE debuff, walk up to point blank and shoot them in their ugly face.
Note, Method Three requires a fairly specialized build to pull off. Method one and two can be done with Automatics or Longarms if your mage is able to cart around a big gun.