Registered RAM's have a ECC (small chip at one side) - error check control.
these are slowers as error checking slows down laetncy process as data has to pass through error check controller. these type of ram's are generally preferred in servers, not in work stations/desktops.
Unbuffered/Un-registered are faster, as they havent got anything like that.
you cannot say that system makes no errors, every system does, as if somehow u control the errors via RAM's what will you do to avoid errors in Processor pipe-lines? install another ECC there?. best is to go with Non-ECC/Unbuffered/Un-Registered RAM's