Regex allow for infinitely more complex matches than other methods. Regex is slower than the other methods for simple matches because it has to invoke a regex object no matter how simple or complex the regex is. Even simple examples of regex are much smaller than non-regex equivalents. Example:
if ($regex(%var,/(alpha|beta|gamma|delta)/)) blah
vs
if ((alpha isin %var) || (beta isin %var) || (gamma isin %var) || (delta isin %var)) blah
Regex is a very powerful tool if you know how to use it correctly and completely. Very simple comparisons are probably more suitable to using the isin method since they don't invoke a regex object.
For more regex info try:
http://www.regular-expressions.info/-genius_at_work
