Simple. if the enemy ambushes all of you which of us is best suited to turning an ambush for example?
3 people who will make so much noise the moment they move in that the enemy will know you've arrived? Or the guy who can drop a squad 1 by 1 in complete silence to open an escape route and plant explosives to distract the enemy when you move.
Of our group my characters skill set is by far the best suited to being the wild card of the group because I have special forces level training in blades, pistols and scoped weaponry and above special forces level stealth and stalking training plus stealth armor as well as demo training. My skill set is the most varied which allows me the most flexibility when reacting to situations.
Look at you 3.
A medic with heavy weapons, good for supporting fire and keeping us fit but limited other uses.
A combat engineer, heavily armed and armored but this also makes him slower and noisy.
Support engineer, very slow, heavily armored, medium armaments and limited support capability.
Each of you 3 is built more as a supporting aspect or as a piece to build a full team, where as I'm built both for support and solo operations. None of you have the skill set to operate alone like I do.
Then mine, medium armed with short, mid and long range capability including AP, HE and HP munitions as well as explosives, lightly armored but with stealth system. Arguably one of the nations best when it comes to stealth and stalking as well as elite level combat training and explosive training.
Of us 4 which one of us will be best suited to moving alone and reacting to enemy threats quickly without causing a bigger commotion?
I can take out infantry, aircraft and vehicles alike completely alone and without exposing the group in the process.
So which of us 4 is best suited to being the wild card of the group and staying unknown to the enemy until they need to move in? As I see is the most important trait for the wild card to have is the ability to remain undetected.