On "Unfriendly Competition" I threw grenades outside the door. And I killed the one's that could attack me with a sniper rifle. The ones in the pool got killed all by one grenade throw, I completed the game two days ago anyways. I did Unfriendly Competition first try, I'm just too good when grenades come, every throw gets around 3 kills. Also on the last part I took out my sniper, zoomed in the dealers head and shot it till his health run out. and WOW! mission passed.
Last Stand was a cool mission too, I killed both of my enemies with a shotgun. Don't really need a minigun all the time