Some commentary:

The Sherman and T 34 represent the two tanks that won the war for the Allies. It is hard to refute their position at the top of the list. The Sherman is basically the equal of the T 34 in armor, firepower, and mobility. The T 34 has a mobility advantage tactically while the Sherman is better operationally and strategically.
The Sherman is clearly the more efficent and reliable of the two. Both had equal impact on events in the war at a minimum. On impact, one thing to remember is that the Sherman served on many fronts during the war in many diverse roles while the T 34 served primarily on a single one making the Sherman truly ubiquitious.

The German panzers come in right behind these two Allied vehicles. The Panther edges out the Tiger on its greater use and near equal capability. The Tiger is put ahead of the Pz III and IV only because of its tremendous impact tactically and psychologically on its opponets. The Pz IV was Germany's workhorse while the Pz III is only marginally less important being the panzer the Germans rode all their victories to.

The culmunation of the British I tank development is the Churchill. It epitomizes the breed and proved its workth in this capacity through the Korean War. The Churchill in its limited role served the British very well in service.

The Stuart represents the sole light tank on the list. It was a solid, reliable vehicle that held its own as a battle tank in North Africa and throughout the Pacific. A very successful if unremarkable design that soldiered on from the beginning to the end of the war.

The M3 Lee - Grant represents an odd design that proved reasonably capable in the West (North Africa) and very useful in Asia where it was used effectively through the end of the war. As an infantry support vehicle it was a solid if ungainly design.

Some didn't make its:

The Matilda II: The Matilda proved very successful for a very short period from during 1940 and into early 1941. Its shortcommings included the 2pdr lacking an HE round, poor reliablity, and low mobility. It was also an expensive vehicle to build. The Valentine, its follow-on suffers many of the same problems but is just enough better that it could serve as a replacement when nothing better was available.

The KV series: Here is a series of tanks that have one redeeming feature over the T 34; more armor. Other than that, they are slow, awkward, lack heavy gun armament compared to Soviet mediums, and are still unreliable and difficult to operate efficently.

The Pz 38t: Not a bad light tank but nothing spectacular either. A bit too cramped for upgrading. The drivetrain and hull did prove exceptional as a basis for many other vehicles. Edged out by the M3/M5 primarily on developability as a tank and longevity / usefullness.

The Crusader and other British cruiser tanks: The Crusader is a much less reliable and useful light tank than the Stuart. Both have almost equal qualities in terms of firepower, armor, and mobility with all three having a sight edge in favor of the Stuart. While later models got a 6 pdr it was really a cramped installation. At the same time the Crusader and other cruisers suffered from narrow tracks and resultant high ground pressure along with notorious unreliability. The follow-on Cromwell and Comet while better, were still less reliable and offered nothing over the Sherman. Cramming a 17pdr on the Cromwell resulted in the ungainly Challenger a much worse conversion than the more versitile Sherman allowed.

None of the French designs in use in 1940 made the list. They were all very deficient particularly suffering from the one man turret design. The Souma 35 was mentioned. It had serious flaws in the hull armor being a three piece bolted design (bolting was a problem common to the Char B1 too). The crew disposition was poor. Short range and unreliability also plagued the French designs.

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