Mainly: what is the best defrag program you can use and why?
YMMV. Defrag programs have their strengths and weaknesses. Some people prefer features (such as individual file defragmentation), some heavy optimization that gives you as much performance as possible, some fast optimization that completes quickly.
Additionally (on the why question), how would someone go about determining the best possible optimization method? I don't see reviews really looking at that -- they mostly focus on the interface and other goodies like zapping temp files or boot-time optimization.
I'm afraid the only way to determine that is to review the claims on the websites of defrag programs.
I'm not aware of any testing program that'd allow you to measure the differences between programs. (Existing benchmarks such as CrystalDiskMark don't simulate real world usage, so they are only suitable for hardware benchmarking.)
For example, here I review a claim at the MyDefrag website:
MyDefrag organizes files into zones, such as directories, Windows files, files used while booting, regular files, and rarely used files. The most accessed files are placed at the beginning of the harddisk, and files that are commonly used together are placed in close proximity to each other.
If MyDefrag can do that, it will indeed increase speed a lot. If files accessed at the same time (such as data files used by same program) are spread very far from each other, the hard drive needs to perform long and slow seeks which take much more time than actually reading the files. On the other hand, if the files are in close proximity, the seeks are very short (and fast) or even nonexistent (if all the files are in the same track).
In addition, MyDefrag should be able to do that. The Prefetch
feature of Windows keeps track of files which each program accesses on startup, so that the files can be cached when the program starts up and the program can access them faster. MyDefrag should be able to parse files used by Prefetch and therefore find out which files should be placed close to each other.