Each with his own I guess. They all have their advantages and disadvantages. Auslogics is really fast and VSS compatible but some feel that the optimization it does is inferior to other products and it also doesn't have a boot-time defrag. I recently had a fragmented MFT and tried to defragment it using Defraggler, Puran free, Smart Defrag free and even a trial version of O&O defrag. All failed to reduce the number of MFT fragments.
Puran defrag is not VSS (volume shadow copy) compatible (I am not sure about the others, except Auslogics, but I suspect they can encounter the same issues). Puran's help file has some recommendations to prevent the loss of shadow copies on disks: format your disk with a cluster size of 16K (not always an option and a "waste" of space, most of us have a 4K cluster size) or disable many of the optimization features.
From Microsoft:
The System Shadow Copy provider uses a copy-on-write mechanism that operates at a 16-KB block level. This is independent of the file system's cluster allocation unit size. If the file system's cluster size is smaller than 16 KB, the System Shadow Copy provider cannot easily determine that disk defragmentation I/O is different from typical write I/O, and performs a copy-on-write operation. This might cause the Shadow Copy storage area to grow very quickly. If the storage area reaches its user-defined limit, the oldest shadow copies are deleted first.
source
System Restore creates shadow copies so using non-vss compatible defragmenters might lead to the loss of Snapshots.
In case you are wandering, I managed to defrag the MFT using DiskTrix UltimateDefrag.
edit: Defraggler doesn't seem to be VSS compatible:
link