How do you express trigonometric identites in simplest form, e.g. $\frac{2\sec(x)}{\tan^2(x)}$?

Question

Are there strict rules defining what the "simplest" form of a trigonometric identity is? For example, $\dfrac{2\sec(x)}{\tan^2(x)}$ can also be expressed as $\dfrac{2\cos(x)}{\sin^2(x)}$ [ignoring restrictions on $x$].

Which one, if either of these forms, is "simpler," and why?