Clowns are nice....definitely, but they get huge. I have read they eat snails too or at least keep the population under control. I've seen them huge though....hope you have the space.
I'd have a hard time making my mind up between sidthimunki's and clowns. You didn't say tank size was also not an issue. With a giant tank it would be clowns. With a not so giant tank it would be sids.