How to choose the best database management system software is an interesting problem and it takes on many different forms. For example, should I answer it based on you having no existing DBMS and you're just looking to buy one for the first time? That is a valid, though not too common, situation. On the other hand, you are more likely asking something like "Which of the several different DBMS platforms that we already have should we use for Project X?" This is also a valid question. So, let me answer both for you.
First of all, if you are brand new to DBMS it would be a very wise course of action to hire a database consultant (or two) to help you with your selection process. There are several very good choices out there. My preference is that new users should generally choose from the market leaders, and that means one of the big three: IBM's DB2, Oracle, or Microsoft SQL Server. Of course, you also have other options such as an open source DBMS like MySQL or PostgreSQL. These are up-and-coming platforms and they can be used for some types of production work (mostly lower-end or simpler web-based development projects). For high-end mission-critical applications, stick with the Big Three.
OK, which of the big three? Well, if you are a large organization with a mainframe and want to run your DBMS on that mainframe, you really should go with IBM DB2. Oracle has a mainframe version of their database server, but IBM is far and away the market leader here. For Unix and Linux installations, your choices are Oracle and DB2. Oracle is the market leader on those platforms, though IBM has a nice presence there, too. For Windows development, all three are viable options, but Microsoft is obviously the leader.
What about other options? Well, Sybase, Informix, and Teradata are the next biggest players in the market. Sybase has lost ground in the market, but their DBMS is still solid and they are firmly entrenched in the financial market. Informix was purchased by IBM and it is still being maintained, but DB2 is obviously IBM's primary DBMS – so I personally would not choose it for new work. Teradata is a high-speed DBMS that is geared for data warehousing and OLAP work and you might want to choose it for those types of projects.
This was first published in November 2005