The line EXECUTE CORRELATED SCALAR SUBQUERY 1
is just there because you're using a different query syntax.
The actual execution is the same in both cases: SQLite goes through all records of the Queue
table, and tries to look up the corresponding record in the LastQueue
table.
That the estimated record counts are different is of no concern to you, because you know that the actual number of records is the same.
Joins might be better than subqueries in other databases, but in SQLite, which uses only nested loop joins, the only difference is that a join allows SQLite to choose the outer and the inner table in the join.
In any case, you should write the query in the most simple and maintainable way, and optimize it only if you have measured that you get a noticeable and necessary improvement.
Please note that instead of:
WHERE (SELECT ...) IS NOT NULL
it would be more idiomatic to write:
WHERE EXISTS (SELECT ...)