If a Mack truck and Honda Civic have a head-on collision, upon which vehicle is the impact force greater?

According to Newton’s 3rd law, the force is the same for both vehicles!

Which vehicle experiences greater acceleration greater?

The Honda experiences greater de-acceleration because it has less mass.  Newton’s 2nd law (F=ma) can be rewritten to read a=F/m.  For the same force the acceleration is inversely proportional to the mass.  Hence the lower mass object (the Honda) experiences greater acceleration which in this case is actually de-acceleration.

Which team wins in a tug of war; the team that pulls harder on the rope, or the team that pushes harder against the ground?

In this case an external force is required to move the both teams.  If one team pulls on the rope with force F1 to the right, then the other team is reacting with a force F1 to the left (Newton’s 3rd law).  The action/reaction forces are internal to the system containing both teams.  To get the teams to shift position requires one team to push harder against the ground so that the ground can in turn push harder against that same team and hence drag the other team into the mud pit.