I've used Perfect Disk, Ultra Defrag III and am now using O&O Defrag Professional Edition 12.5.
I like it since they have the COMPLETE type of defrag that sets the harddrive (works best for the systemdrive) into three zones.
Bootfiles in the first zone.
Installed stuff in zone two.
Everything else in zone three.
This is supposed to be better than what other defraggers do but I'm not sure....a defrag takes like 30min but it's never 'done'. It also hangs often.
In the zone options there's this option of putting every file that's bigger then x into zone 3 and so I've put it at 1GB (default was 512MB). Hope it was the right choice but I'm a bit afraid that I'll mess things up.
I used Ultra Defrag III before but that program had many options which I never understood nor did I WANT to take the time to understand everything about it.
My systemdrive has lots of games and programs installed and that's the drive that's important.