Shoutcast Servers
Pro's :
Your station is listed on Free Internet Radio - SHOUTcast Radio - Thousands of Free Online Radio Stations and syndicated out to many other radio directories. This gives you excellent exposure and will likely lead to getting more listeners than you would do on an icecast server.
You can ban listeners by ip or subnet.
Con's :
If you plan on running an Auto DJ on your radio server then when you want to play live you will have to turn off the Auto DJ server and then on again when you have finished.
Icecast Servers
Pro's :
Icecast has mountpoints meaning and automatically transferes listeners from the Auto DJ to the Live stream and back again without needing to manually turn anything on or off. So you connect and all the listeners are transfered from the autodj to the live stream and then back again when you are finished.
Con's :
You are listed on Streaming directory -- streams & radios instead of shoutcast.com which gets fewer listeners tuning in than a shoutcast server would.
Conclusion : If you plan on running an Auto DJ and doing live streams then the ability to auto-transfer listeners is very useful and worth considering an Icecast server to do. If you only plan on live streaming with no Auto DJ then the extra listeners you get from shoutcast.com it would be worth using a shoutcast server.