My personal choice would be the serpent star and for a number of reasons. The brittle stars arms tend to fall off alot(hence their name) The one in my moms 24 gal
was always losing arms. As long as you have plenty of LR
the serpent will be a great choice. They are awsome at cleaning up any leftover food and are swift movers. I have no experiance on the orange star but I can vouch for a red sea star instead. I have one thats is about silverdollar size, beautiful addition(been alive for 2 months so far).
Your tank might be to small for a sand sifter. Unless you have tons of sand surface on your SB.
I think the best thing for your tank would be a single serpent star.
3' fine sand bed 1x Orange Stripe Prawn shrimp goby, 1x sixline wrassemated pair of true percula clowns, 1x CBS shrimp, 2x peppermint shrimp, 1x pistol shrimp, 1x tiger tale cuke
, ~20+ snails, ~10+ hermits, 1xserpent star.
green Bubble coral, hammer coral (8 heads!) ,various Zoos,green finger leather, green star polpys ,shrooms
175w 10k MH
28w actinic 03
2x maxi jett 1200
Prizm skimmer (modded)
Hagen powerfilter(for running carbon 24/7)
nano arctica chiller