In a Vs. type situation, Scorpion wins 7 times out of 10, I'd say. Simply because of more powerful shots to take the Mantis out at considerable range. On your average map where you don't have to worry about them going up against each other... I'd say Mantis. Against a Wraith, the added speed and smaller target would help avoid the mortar shots. Against your average person on the ground, it is almost impossible to take one down without some sort of power weapon, since it has its own rechargeable shields to get through before damaging the vehicle itself. Add in rockets that can home in on vehicles, and a pretty powerful machine gun, and the Mantis is certainly something you don't want to come face to face with.