When scripting, which is better?

Hi all,

Reading through the script files again, there seems to be several
different methods of doing the same thing :

i.e. if [ -x "$self_path/postmaster" ] && [ -x "$self_path/psql" ];
then

or

if [[ -x "$self_path/postmaster" && -x "$self_path/psql" ]]; then

if [ x"$foo" = x"" ]; then

or

if [ "$op" = "" ]; then

or

if [ "$foo" ]; then

--
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi