Who's your favourite (or not) sand sifter ?

[Reef Pilot]

In my other display tank, I have 2 fighting conch, and used to have a tiger conch, but he died. They move around a bit, but don't do much to clean the sand that I can see. Keeps my Copperband interested, as he tries to pick under their shells. Not sure if he is looking for food there, or trying to get at the snail itself. Not sure why the tiger conch died (might have been the Copperband bothering him), but he didn't move for a couple days, and when I picked him up, it was a really bad stench, so I knew he was dead.

But for sure, my gobies in my other tank, do a much better job of keeping the sand looking clean and fresh.