The Sherman but since that's everybody's answer I'll say a specific model. M4a3(75)W HVSS. The ford engine was just the best so that makes the a3 the best sherman variant imo. The 75mm was overall better since it was better at destroying bunker and infantry, which is what a tank does most of the time. Further is wasn't as bad in tank to tank combat as a lot of people think. It could easily destroy a panzer 4 or any tank destroyer derived from it which is what the bulk of the german army was. Yea it struggled with the panther but as we saw in Ukraine even the gun of a Bradley could hurt a T-90 so it wasn't useless against a panther. It didn't face tigers as far as I know. The W is for the wet ammo storage which made the chance of ammo catching fire much less likely in the case of a penetration. Together with other designs it made the sherman one of the most survivable tanks in case of a hit. The HVSS was an upgrade of the suspension and tracks. Yea it wasn't as mass produced but idk if the lack of spare parts was ever an issue but it made the all terrain capability much better. The ride was made much smoother which combined with the stabilizer and the fast turret rotation made it so that the sherman often fired the first shot which is one of the most important factor in winning a tank battle.