I have a fixed (rarely changing) list of ~100 words. I want to display a random word on my HTML page on every reload. Should I hardcode the words as an array in the PHP script, or should I put them into a MySQL table and pull a random entry from there? What are the possible performance/maintainability considerations here?
It depends, if you ever want to easily manage these words or have someone else manage them, I would go for putting them into a database. Using a database has an extremely high overhead relative to a PHP array, although it is likely unnoticeable for a human if hosted locally.
I would not use anything other then a PHP array, database table, or text file though. I think that even a text file is a little bit extraneous and shouldn't be used - if you would want it in a text file it's probably just best to put it in a database.