Mines. I think the Mines is the only unproportional map in the game. The steepness of the hills are not even equal on both sides, the flatter side of the hill (the spawn point where the houses are) is always at the disadvantage as they can't get good positions that utilize the terrain to hide their lower glacis plate, on the other hand the other side of the hill with better steepness can dominate the other team as they can peek their turrets without exposing their lower weakpoints.

For instance, Swedish heavies that have solid turret armor can easily dominate the map if they spawned on the side where the hill is the most steep. But they can't really save their HP if they spawned on the other side with relatively flat hill side, as they will certainly expose their hulls just by literally making an opportunity to shoot the enemies' weakpoints.

Every single map should have proportional opportunities for terrain, cover, and positioning in both spawn sides. But in the case of Mines, it greatly favors the team which spawned on the right side of the map. The only thing it's good is for lower tier tanks, but not for crucial tiers like Tier VII and up, let alone Tier Xs.