When you need big, bad and ugly it is hard to go past the ISU-152.

This tank destroyer is designed to sit in a concealed position and destroy enemy tanks whilst being impervious to enemy fire thanks to a survivability stat of 2. Fortress, which helps to keep the tank safe when being shot in the side, and the benefits of being a Tank Destroyer which improves the tanks survivability when concealed. If there is one downside the ISU-152 it would be the relatively low initiative, but this can be improved by adding Situational Awareness to your radio operator.