The ports between 49152 - 65535 are recommended because there seems to be less chance of ISPs blocking those higher ports. If the port test
http://www3.limewire.com:6346/
works ok & you don't think you have an ISP problem, you can use the default port of 6346 (I do). Or you can try any ports in that higher range.

Just remember that LW's listening port, port in the 'manual port forward' box & port forwarded within your router setup should all be the same number