I have been using Auslogs Disk Defrag for some time. It works well. The main reason that I used it was that it is much faster that the Windows build-in defrag.
Recently I found another free program that is even better. It reminds me of an old-time program called (VOPT) which is still around as version 9+. It is not a free program.
IObit Smart Defrag 1.02 does a far better job of eliminating scattered packets that remain after most defrag software has finished. It concentrates virtually all of the data at the front of the disk when using the "defrag and optimize" setting.
This is one of those time that I say, "Trust me and give it a try".
More info - http://www.iobit.com/iobitsmartdefrag.html#
Additional download site MajorGeeks - http://www.majorgeeks.com/IObit_SmartDefrag_d5318.html