Transferring iMac's HD to a new, ( old ), MacPro....

I have a 2009 iMac 27" machine that's running OS X Mountain Lion and I will soon be getting a "new" refurbished 2010 Dual Processor 12 core i5 Mac Pro desktop to which I want to transfer everything I have on the iMac, and I mean everything including visible and invisible files. The Mac Pro will also have Mountain Lion installed as it's OS and for now that's the OS X I want to stay with, not upgrade to more current OS's.

Would it be better to use Carbon Copy Cloner or Superduper or use Apple's Migration Assistant? If so how?

I also have current Time Machine backups of the iMac's hard drive made to an external HD.

What I want to make sure of is that everything is transferred to the "new" MacPro's primary drive including all application registrations and so on. This is the most important things for me, I don't want to have to go through re-entering my registration codes for the applications that I presently use on the iMac. Went through all that before and it was a royal pain, trying to avoid that this next time.

Or rather than cloning the iMac's internal HD to the MacPro's HD as the incoming machine is a MacPro and has four HD trays would it make sense to make a clone of the iMac's drive to a newly formatted hard drive in an external HD dock then simply put that drive into the MacPro and boot up?....Would that work?

If anyone's gone through this process successfully I would really appreciate any advice and tips as to best go about this before I completely mess it up!

Thanks!

PM