The answer depends on what you call default so i will just skip that word and use Priority instead
The Generator has priority
That means if the generator is running, THAT is the power source.. If the generator is NOT running, then Shore power is selected on a two source switch,
On a 3 source switch, Generator has priority, then shore power, and the last to be chosen (if no other source present) is Inverter.
NOTE: Shut down A/Cs for 3 minutes when transferring, shut down all big loads, and if possible all loads, before transferring.
(The 3 minutes, shut down, transfer and when 3 minutes is gone by re-start). Other loads Shut down transfer restore. (no need to wait)