Its going to depend on when Japan intends to declare war. Â If they J1, they get to kill an UK BB, a US fighter, destroyer and sub, and can begin the game by taking all of UKPACs income.
However, a J1 doesn’t give Japan any time to build up and so it can invite a strong KJF in response, by moving (and building) everything the US can right onto your doorstep. Â Later Japanese attacks on J2 or J3 are more conservative, but the UK and ANZAC get to grab much more income in total, and the Americans still get their bonus income.
So, the answer depends on Japan and what that player has in mind for their strategy.