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.
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.
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?