How does Storj decide what region and node to store my files?

Yes, I’m talking about uplink CLI or rclone or FileZilla, all other (except backup tools and Nextcloud) mentioned in our documentation uses GatewayMT.
From mobile apps I know only about this one: https://play.google.com/store/apps/details?id=com.storj_mobile
The Photos+ uses GatewayMT as well.