What is the fastest database system?

I'm planning to renew my administrative applications in my bussines, the main database is populated with about 500, 000 records and I'd like to know what kind of database system is better for a database that large. Some ppl have offered me new applications based on access, sql, mysql, paradox, etc. Which is better and why? The one I use is kinda old, but really fast......btrieve