My grandpa prefered the Americans, because the local soldiers gave him (and the other kids) sometimes sweets or stuff like an orange (which he thought was a ball at first, being disappointed that it didn't bounce :D) and were generally very nice to them.

Some older kids only wanted to play as the Germans or Hungarians (at the end of the war, apparently some Hungarian troops were stationed in the local bunkers to fight off the Americans).

I don't know what the other kids in his age group prefered, though.