Pls. Help Me to Back-Up my All Important Files Using SuperDuper !!!

[jojhubhang]

I'll appreaciate all of your response here.
This is my scenario, I have an external hd with a total capacity of 232.76 GB
I have old backed up files already in there from 2 years ago
(my last backup after a big crash an loss of data)

I have 75.65gb remaining on the external and 40Gb remaining
on my internal HD. I have some corrupt files and want to do
a back up before I run a anti-virus program.

I don't know which back-up to choose. I'm afraid to do the erase back up. Because
there may be stuff in there from my former computer, I don't know.

I don't know if the smart update is enough or if the newer or different
file options are too much. My space is limited. What do I choose
if I don't want to double up on any of the old info and don't want
to loose any of the old info? Do you think I am being overly
cautious? Please help, I am computer illiterate for the most part.