Best Artillery piece:
I actually agree. The 88 was a killer; effective against damn near everything possible.
Again, I agree; though in comparing the 9mm Luger against the colt, It'll be a difference in accuracy and range vs stopping power. Both are sidearms, however, so don't expect much of either. The 9mm is a higher-velocity round, with a flatter trajectory; whereas the .45ACP was a low-velocity, high weight round. I have no experiences with the TT-33 or Webley, or any of the minor players' side arms, so I can't really compare them.
T34/85 was the best tank. It was reliable, reasonably well armored (it's still a medium tank), and had a powerful gun. T34 in whole was not, as the older model T34 were much poorer tanks, and at the time they were fighting they would not match up to a Panzer IV.
Best Infantry Support Weapon:
The Browning MMG. Variants are still in use by the US Military; which have very little differences to the WWII guns. The .50 BMG used today is effectively the same MG.
Best all-round aircraft:
P51 Mustang. Don't ask me why; I'm not much into aircraft.
Best Infantry Rifle:
M1 Garand. Obvious reason is that it was reliable, accurate, powerful, and when the US entered the war it was the only Semi-auto in service. And I seriously doubt that the en bloc clip ejecting would have made that much noise compared to the machine gun, rifle, and cannon fire in actual combat situations.
Best Squad Support Weapon:
Browning Automatic Rifle. Only disadvantage was it's 20 round clip. As accurate as a rifle, and capable of providing excellent suppressing fire against entrenched positions.