While getting a bit long in the tooth, soulseeX still is a great client, the best Mac Soulseek client there is. Unfirtunately it doesn't seem to behave well for some random users. There's one thing though, that you have to try first, if ssX keeps on filling your HD: Turn off logging in ssX. An application restart once on a while won't hurt either.

The developer is busy keeping the slsk server running and also contributing to the further development of the official (Windows) slsk client. Expect ssX to be updated after that is out of the way. When will that be? Dunno, maybe in 6 months, maybe in a year, but meanwhile I'm still (after >3 years of usage) happy with the current release.