Of the dead eye cards, I've Paint It Black (paint targets onto enemies), Slow and Steady (take much less damage, headshots don't kill you outright, can't run or sprint) and Slippery Bastard (neither enemies nor you can lock onto each other) fully upgraded, and I switch them to fit the situation I'm in.
As for the passive ones, I'm running with fully upgraded cards that focus on damage, Necessity Breeds (as you get closer to death, you start to do much more damage) and Winning Streak (each
Dead Eye Ability: Slow and Steady III
Passive Ability: Winning Streak III
Eye for an eye III
Never without one III
Honestly, you don't need Never without one 3, 2 is just fine. Same goes for Slow and Steady 3, 2 will do just fine if you want to save $1,000.
Here's a complete list of the Ability Cards and what they do (all listed at level 1)
Dead Eye Abilities
A Moment to Recuperate: While Dead Eye is active you slowly regenerate health. Taking any damage will cancel Dead Eye
Focus Fire: While Dead Eye is active you and your team members deal a little more damage. If more than one member of your team has this ability active the effects do not stack.
Paint It Black: While Dead Eye is active you can paint target onto enemies. Fire