It doesn't matter how fearsome your weapon is if you can't get it to the battlefield.
Absolutely spot on. "strongest" tank of the war for me was therefore unquestionably the Sherman in all its guises.

Not that I would have fancied being IN one in its tommycooker days, but then the early T34 had a lot of problems too. (Blindspots out to 200 yds? One man turret? No radio? No thanks)

Here's a random thought: how about the Matilda? Entirely impervious to 37 and 50mm AT fire, and withdrawn from service before 75mm guns came in. Survivability is looking good...