sc_trans and ices are both streaming source applications, which provide an audio stream to your ShoutCast or IceCast streaming server.  Unless you're doing anything really exotic, sc_trans and ices essentially serve the same purpose, and they're both free to use.

ices is an open-source package, and works with both ShoutCast and IceCast.

sc_trans is proprietary and closed-source, and only works with ShoutCast.

In our experience with real-world streams, we have found that ices is significantly more stable and reliable than sc_trans -- the latter tends to crash frequently for no apparent reason with certain MP3s -- and as such, we tend to recommend ices for use on production streams.