Comparing Query Performance Across DBMSs
I think that you shouldn't rely on any of that. The only real measure is how long the query actually took, when measured from the client side. That also avoids overhead during query execution that you get if you for example use EXPLAIN (ANALYZE) in PostgreSQL.
So I would do it like this:

measure the current time on the client

send a query to the server

wait until execution is complete and the client has got the result

measure the time again and calculate the difference