We spent over 45 hours researching and testing the best disk defragmenter software. The best choice is O&O Defrag. This software offers tools for defragmenting your HDD while optimizing your SSD devices as well as overall performance. From the program’s dashboard, you can view recent and lifetime performance statistics and watch over the scanning and hard drive defragmentation process. You can easily schedule a customizable single or recurring scan, whether it’s at night while you sleep or while you use your computer with the resource-throttling option turned on.