avoid the twin spot unless you have a very mature sandbed with lots of life. they are kinda like mandrines in there feeding needs, but they dont eat pods.
my fav SS goby is the sleeper banded goby (Amblygobius phalaena). they too need a mature sand bed but fare much better than the twin spot and they dont make big piles of sand like its cousin the Valenciennea. great personality too.
the watchman will only keep his hole clean.