This discussion goes around and around.
For this discussion I am trying to generalize across the board. I am not pointing fingers at any individuals personsal taste. Nor am I discussing actual events in history.
Based on the human nature to always be better or have better. Discounting pilot ability and refering to fighter aircraft capabilities only, here is my take.
If you prefer the early set, you prefer the Axis planes (Japan, Italy and Germany). These countries were the aggressors and had much more capable aircraft from the onset of hostilities.
If you prefer the early mid set, you still prefer Axis planes. The Allies advance against Japan dramatically, due to plane armor and speed.
If you prefer the mid set, you still prefer Axis planes. Although Germany remained the most advanced, Japan and Italy begin to lag. The Allies made strong gains, particularly Briton, but the advantage still goes to Germany.
If you prefer the mid late set, you prefer Axis or the Allies. Germany holds techological advantages, but no decisive advantages in capability.
If you prefer the late set, you prefer Axis or the Allies. Propeller driving aircraft pretty much even out for all countries.
If you prefer the late late set, then you (and everyone else in the arena) would chose Germany. Jet aircraft, particularly the ME-262 totally dominate.
The late late period was almost the height of piston engine propeller driven aircraft technology. I very exciting time in aviation history.
Basically Germany and Japan were the primary agressors, and were VERY prepared to fight and to dominate. For the most part, Germany had more capable aircraft throuhout the war. The Allies were hard pressed to play catch up. Especially during the early periods.
I am only one, but I think HTC has done a remarkable job at balancing this all out. The main arena can't compare to real war. I see a good mix of planes in combat and generally things seem pretty balanced to me.
Just somthing to think about!

Mino