Difference, like most computer related things, comes with preference. O&O, diskeeper as mentioned is good. I've used Perfect disk in the past, had a lot of good features and techniques to it. Really, the windows one will do unless your an anorak.
There are many opinions on this one. I have tried several and ended up using two; for 'everyday' use I run Advanced System Care Pro click here with the defrag facility enabled, and for a more 'in depth' defrag I run Auslogics Disk Defrag click here