If you were picking...

[GreenHornet]

Depends on the type of battle you're talking about.

For armored battles -

CMAK I'd go with the British in mid/late '41 since nothing can touch the Matilda III or Valentines. Or else pick the Germans in June '42. The Allies have very little that can handle the frontal armor of the Panzer IIIJ or IIIL.

CMBB I'd pick the Germans in mid/late '43. The Russian T34's can't penetrate the 80mm frontal armor of the Sturmgeschuetz IIIGs.