Diskeeper is the same one that is built into Windows XP it's just trimmed down to remove some of the automation stuff.
I used to use Diskeeper but wow their marketing machine is too much, on the verge of a full on SPAM machine.
I use Perfect Disk 8 right now as they actually have some better benchmarks than Diskeeper and are much more liberal on what you can run it on. Diskeeper charges you extra if you run it on TB file systems which is a crock of $#%@%^
All in all they're all quite similar and all use the built-in MS API calls to move the files around so not like one is SOOOO much better than another. Some just have other features than others and some have better pricing models
