M26 does not really have a clear advantage over Tiger II and KV-1, even though it's the last tank to be unlocked as of march 2014. It's accuracy is good at 39 points, but this decreases as the gun is upgraded.
Pershings cannot compete with Churchills and Tigers against their health and armor, but a smaller frontal profile and slightly greater top speed gives it the edge, especially in mid range engagements. It's 90mm cannon have slightly better firepower, but similar reload speed.
The M26 is not really a rage charge tank because of weaker armor, Use it as a marksman tank at medium range, pick off damaged or weak enemy tanks and when opponents heavies come, fire a shot, retreat behind cover, the shoot again, remember to use the Pershing reload speed advantage over KV-1 and Tiger II. Fire at them and they'll return fire, but you can be ready for the second shot while they're still busy.