Where British cruisers would reinforce the US Pacific war
Additional British County-, Town-, and Leander-class cruisers would be useful throughout the Pacific, especially where Allied forces were short of ships in the Southwest Pacific.
Where could the US Navy best use four County-class, six Town-class, and four Leander-class cruisers in the Pacific?
Short answer
They would be useful across the theater, but especially in the Southwest Pacific, where Allied forces were repeatedly short of ships.
Notes
In this counterfactual, British cruisers could find employment throughout the Pacific. The Southwest Pacific stands out because Allied operations there were repeatedly short of ships. Australian cruisers already participated in the region's battles and provide a comparison for the proposed reinforcements.