How important is code readability versus performance optimization when choosing variable names in PHP?

When choosing variable names in PHP, code readability should be prioritized over performance optimization. Clear and descriptive variable names make the code easier to understand for both the developer and future maintainers. While short variable names may slightly improve performance, the trade-off in readability is not worth it in most cases.

// Good variable naming for readability
$userName = "JohnDoe";
$userAge = 30;

// Poor variable naming for performance optimization
$un = "JohnDoe";
$ua = 30;