Not sure, haven't quite used both, but I do use Diskeeper and I give it 5 starts. It gives excellent defragmentation, defrags your page file and MFT zone, does realtime defragmention in the background, consolidates free space, and places similar directories in same places on the hard drive to reduce latency when they are read and stuff. Definitely a performance increase overall. However i can't say anything about O&O defrag...haven't used it.