It really depends on several factors. What you are planning to do with the database is the first and most important one. If you're gonna store a few million records for a dozen users, then both are quite capable of handling the load and are rich programmable dbms environments.
If you are gonna build a transactional system with failover, need pre-built software packages for accounting, and need a commercial support contract to proceed, then Oracle is gonna win.
If you are building black boxes that just server data at a customer site and you never wanna have to touch it again, I'd use postgresql and put a 'vacuumdb -a' in a nightly cron job and you're done.
