Giles is a really good lightmapper, it is dedicated to doing just the one task. However, I'm not sure whether the current dbo export is working correctly.
I haven't used the 3DWS lightmapper, but the advantage there is that you can model and lightmap in one program.
DarkLIGHTS is different, it allows you to lightmap programmatically. Hence, you can create your scene dynamically (place objects randomly, for example) and create a new lightmap in your game. You can also allow the user to create their own scenes and then build the lightmap.
