I would like to know and what is the best besides the price

MySQL seems like the one that's used most often. It's pretty fast, but it doesn't have the features some more advanced RDBMS systems have. If you need stuff like subqueries, etc. and can't afford to pay more than $0.00, PostgreSQL might be a better choice. :)

I heard DB2 was the most popular Database out there

DB2 is popular, but with web-based applications mySql is more popular. So I guess its a relative term depending on what you're using the database for.

Are we talking web or overall?

I think web based MySQL is probably the most common out there but, in use maybe MSSQL or DB2 (not really sure)

I'm about 70% sure that the most implemented database is probably Oracle (judging by their stock price :cool: ) in for the entire IT field.