PHP: strftime(), date() or DateTime, Which is better?

Question

I am curious to know if there is any advantage in PHP of using strftime() over date() or vice versa.

A class I downloaded used the strftime(). However, since it does not support all time formats on some systems, I want to change it to use date() instead. I was wondering if there are any major differances or advantages in using one over the other.

What about the fact that strftime() only supports date formats that are supported by that servers c library? Does date() have any similar restrictions?