In the original Night of the Living Dead, Ben (Duane Jones) didnt let segregation and race hinder him from doing what was necessary to survive. The strong-minded man kept calm and collected while everyone else was overreacting and foolishly making poor decisions out of fear and confusion. Bens ability to captivate a group and pull them together to work on reinforcing their fortress against the undead, are major leadership qualities that would help to unify your survival group and have you working as a team.
Although Roger was my favorite in the original Dawn of the Dead, his cockiness and selfishness got him killed too soon. Peter (Ken Foree) on the other hand, remained vigilant and stoic throughout the ordeal. His compassion and moral standing made him willing to put himself on the line for the sake of others. His character, along with his military background as a SWAT, makes him an ideal person who you would want fighting by your side. When the going gets tough, its nice to know that the person beside you wouldnt stab you in the back in order to save himself (Ahem, Shane).
Stephen (David Emge) isnt exactly a fighter and he probably couldnt protect you from the living or the dead, but he does know how to fly.
In Dawn of the Dead, Stephen was responsible for getting his group out of the crowded city and into the infamous shopping mall. When the streets eventually become overrun and a car will only get you so far, having someone on your team who knows how to get you around in other ways is vital.