Hi Andre,
other tests, that are not pure opinion or how-to-use, are hard to find. The last one I stumbled over was this one:
http://www.gamingpcbuilder.com/how-tos-guides/free-disk-defragmenters-tested/However, they seem to have used the "Defragment Only" script of MyDefrag. They never published the comment where I asked about it and there is still another comment asking about the defragmenter settings - still unanswered.
I'm also not aware of any major breakthrough in defragmentation software, so my tests should still be valid. I'm using still MyDefrag and additionally WinContig (much faster when you have a lot of files and only want to defrag).
If you want to spend money, don't buy software, buy an SSD instead. I'm never buying a PC or Laptop without one.