Tiger and Panther are indeed very good tanks. I guess "the best" term here needs to be defined more precisely. By important individual capabilities, such as firepower and protection, the answer would be one, and by overall effect on the war and cost-effectiveness, another.
The title "Best
all-round" would require the vehicle be a highly effective combat machine, easy to produce in large numbers, and easy to maintain in the field under combat conditions. There are three legitimate contenders under this criteria: the PzKpfw V Panther, the T-34 (both the 76mm and the 85 mm variants), and the Sherman (in 75mm, 76mm, and 105mm flavors, as well as the 17-pdr armed Firefly plus the 90mm-armed M36B1 Tank Destroyer.)
The PzKpfw VIe Tiger I and the PzKpfw VIb Tiger II, despite their infamy, were produced in far too small a quantity (less than 2,000 of all variants) and were possessed of too many operational limitations (whatever their
tactical advantages) – the Tiger II, in particular – to be considered best all-round.
The PzKpfw VII was a Hitlerian pipe-dream.
Of our contenders, the Panther rates highest in combat effectiveness. Its 75mm/L70 main gun was perhaps the best tank gun of the war. Its well-sloped heavy armor gave it protection better than the T-34 or the Sherman. It possessed better maneuverability than the Sherman, though not quite as good as the T-34.
It was not without its shortcomings, however. It took up great resources developing and retooling factories to manufacture that
may have been better utilized producing many more of the less potent, but not unworthy, PzKpfw IV. It was also maintenance intensive, requiring proportionally greater amount of time in the shop for an equivalent amount of time in combat than either of the Allied tanks. Finally, the Panther suffered fatal reliability problems in its early makes which were addressed, but never fully rectified.
The T-34 was not as effective in combat as the Panther, but it was no slouch. It was extremely mobile for a tank of its size, armor, and armament. Its sloped armor and main gun extending beyond the front edge of the vehicle were truly revolutionary. It was easy to manufacture and maintain.
The Sherman’s faults are fairly well known, but I think it gets shorted in the conventional wisdom. Its reputation as a “Tommy cooker” was an unfortunate reality as was the ineffectiveness of its 75mm main gun, but later models went some way to rectifying this. Wet storage of ammo and a redesigned turret with a loader’s hatch improved crew survivability in later models. The basic soundness of the Sherman’s design allowed the 75mm to be replaced by a high-velocity 76mm gun, a 105mm howitzer, the 17-pdr of the Firefly, or the 90mm gun of the M36B1 TD.
Where the Sherman comes into its own is in the operational sphere. Its ease of manufacture, reliability, and ability to keep going with little maintenance meant commanders could be confident that their armored units would be able to actually put tanks in the field and that said units could be reliably shifted to where they might be needed.
Some numbers will round out the Sherman's (and the T-34's) operational/strategic advantages over the tactically superior Panther.
Numbers built 1/43 through 1945:
Even accepting the supposed need of a 5-to-1 advantage for the allies to take out a Panther, both the US and the Soviets comfortably surpassed that ratio with numbers to spare.
On the maintenance front, I remember reading back in my Advanced Squad Leader days that it took nearly
an hour's maintenance to keep a
Panther in the field for an hour. That same hour's maintenance gets you
8 hours of operation in a T-34 and
40(!) from a Sherman. (Sorry, no idea where to find the reference.) In line with this, Steven Zaloga in
Panther vs Sherman: Battle of the Bulge 1944 points out that at the December 1944,
55% of 235 surviving Panthers in the Ardennes were
down due to mechanical failure/battle damage while only
9% of 1,085 US 1st Army Shermans were lost to mechanical failure/damage.
As the best tank is the tank you have on hand, the above puts a serious dent in the Panther's claim to being the best. Tactically, the Panther is generally considered to be the best tank of WWII, but it had distinct disadvantages at the operational level. Operationally/strategically, the Sherman wins by a considerable margin, but it had distinct tactical disadvantages, especially in its early models. The T-34, while not as optimized at either the tactical or operational level as the Panther or the Sherman, lacks any glaring flaws, so it gets my vote as best all-round tank of the war. I would even place the Sherman ahead of the Panther as a war-winning machine, though I would far rather serve in a Panther myself.