I have found that while the Carolines is sometimes useful, Queensland is just as useful – it threatens the Dutch East Indies, allows the US to shuttle ground forces to mainland Asia, threatens the Phillipines, and allows me to move back to Hawaii in one round. Now, all this is true of the Carolines as well, but:
1. The positioning of US forces on the mainland is different (Malaya, Siam, Shan State, and French Indochina) than if the US had the Carolines. So, the Carolines vs Queensland is a call I make based on what Japan is doing.
2. Queensland threatens more of the Dutch East Indies than Carolines.
3. Queensland forces Japan to come out to engage the US if they are so inclined. This means that unless it does everything perfectly, Japan opens up opportunities for the Allies. It’s also out of range for newly built strategic bombers built in Japan, which can change the fleet balance very quickly…
Early in the game, when the US is not yet at full strength, I go usually go Queensland. Later, when I want to threaten the Japanese directly, I take Carolines (or I may bypass it completely and go straight for sea zone 6 and Korea).
Marsh