Systems which supports both upper and lower-case characters are usually case-sensitive: before testing for the presence of particular keywords or commands it is usually best to convert the an input string to a standard case, usually upper-case. Unfortunately there are no standard intrinsic functions to do this, though many systems provide them as an extension.
In character sorting operations where the strings contain mixtures of letters, digits, or other symbols, you should use the intrinsic functions to make the program portable. In other character comparisons, however, the relational operator notation is probably preferable because it has a more familiar form and may be slightly more efficient.