When the system checks to find the MVP of a battle, it will calculate all the kills of the players and all their casualties.
Kills work positively and casualties negatively towards the determination of an MVP award.
Also, each unit has a different kill/casualty weight depending on its type and its level.
Taking all the above into consideration I will give you an example:
X player kills in a batle 10 Infantry troops of level 1 and loses 10 Infantry troops of level 2. Y player kills 5 Heavy Infantry troops of level 2 and loses 10 Infantry troops of level 2.
If you only look at the numbers, then X player should take the MVP. However, due to the fact that Y player killed higher level and unit type troops, he gets the MVP.