I agree and apologise for writing bigserial out of ossified habit. Identity columns hew to the SQL standard, bigserial is a pg-ism. I actually do still use it when the ORM’s DDL generator prefers as much (looking at you Rails), there’s no gain from fighting the middleware.

For other readers: the two are almost the same in behaviour, they differ primarily in that identity columns don’t need a USAGE grant on their associated sequence, and the ALWAYS makes it harder (but despite the term not actually impossible) to override the default value on row insert.