I like O&O, really i do. Infact it's one of my all time top 3 favorite defrag programs. The GUI is very nice as you can click each block and it shows you which files are occupying it, that is really cool and i wish PD would have this aswell. It was also damn fast on my machine and for that i give it a big plus. It's best feature though has to be the AUTO Defrag option, really i don't know of any programs that have this implemented any better. It really is one of those "install & forget" programs and that's a good thing in my book. Hats off to the developers for making this. As far as defragging goes, it gives you alot of different optimization strategies plus it has a boot time defrag which for me always was damn fast. Some folks said the boot time defrag is slow with this one but honestly on my machine it was bloody fast. Faster than PD for sure, same goes for the regular defrag(though PD does get faster with every defrag). It also takes the layout.ini file into account(you need to enable this in the settings though) so it doesn't screw up the boot time of your pc, that is something i consider very important myself.
So it does have some advantages over PD for sure(it's faster IMO has a more usefull GUI and has a better auto defrag feature) but when it comes to optimally placing the files for faster access on the disk i still think PD does a better job with it(repositions the MFT and is the only defrag i know off that completely defrags all NTFS metadata files). That is what makes PD stand out over the rest and is the reason why i like it so much, it's also the best at defragging boot files and it shortens the boot time even more than other programs.
BTW guys, you should also check out Puran Defrag my 3rd favorite commercial defrag, seriously it is a very very powerfull product and it allows you to SCHEDULE boot time defrags which i think is very cool. It also has a very smart optimization strategy, one which i feel can rival anything out there. Seriously good program. The price is very low aswell.
http://www.puransoftware.com/Puran-Defrag.html