<p>We're living in a golden age of databases, with numerous high quality commercial and free databases.  This is great, but the downside is there's not a simple obvious choice for someone who needs a database for his next project.</p>

<ul>
<li>What are the constraints/criteria you use for selecting a database?</li>
<li>How well do the various databases you've used meet those constraints/criteria?</li>
<li>What special features do the databases have?</li>
<li>Which databases do you feel comfortable recommending to others? </li>
</ul>

<p>etc...</p>

I would think first on what the system requirements are for data access, data security, scalability, performance, disconnected scenarios, data transformation, data sizing.
On the other side, consider also the experience and background of developers, operators, platform administrators.
You should also think on what constraints you have regarding programming languages, operating systems, memory footprint, network bandwidth, hardware.
Last, but not least, you have to think about business issues like budget for licences, support, operation.
After all those considerations you should end up with just a couple of options and the selection should be easier.
In other words, select the technology that suits the best the constraints and needs of your organization and project.
I certainly think that you are right on saying that it is not an obvious choice given the wide number of alternatives, but this is the only way I think you can narrow them to the ones that are really feasible for your project.