<p>In our place we're split between using mysqli and PDO for stuff like prepared statements and transaction support. Some projects use one, some the other. There is little realistic likelihood of us ever moving to another RDBMS.</p>

<p>I prefer PDO for the single reason that it allows named parameters for prepared statements, and as far as I am aware mysqli does not.</p>

<p>Are there any other pros and cons to choosing one over the other as a standard as we consolidate our projects to use just one approach?</p>

Moving an application from one database to another isn't very common, but sooner or later you may find yourself working on another project using a different RDBMS. If you're at home with PDO then there will at least be one thing less to learn at that point.
Apart from that I find the PDO API a little more intuitive, and it feels more truly object oriented. mysqli feels like it is just a procedural API that has been objectified, if you know what I mean. In short, I find PDO easier to work with, but that is of course subjective.