US Virginia, because Heroku users migrating to Render want to test their Render apps against a Heroku us-east1 DB before moving data over.
Which AWS/GCP regions do you typically use for Spain?
This is the first time I'm targeting the Spanish market so I don't have experience with AWS from there. Paris is geographically close so I imagine that would have the best latency (sorry I can't give you anything concrete).