Does anyone know if someone has done a comparison of the backup softwares?
I have been looking up on the web, but there are so many of those software?
I am trying to implement a data backup from different systems in my organization. Amanda seems to be my first choice right now.

As you say, there are *lots* of different products, partly because there are lots of different approaches for different needs. The leading authority on UNIX backup is W. Curtis Preston, so I'd recommend looking around the site he maintains:

http://www.backupcentral.com/

Alternatively, try posting on an admin forum (like the Enterprise forum on this site) with a brief description of your requirements, and you can get a good shortlist of appropriate products.

There is actually a comparison table here: http://wiki.bacula.org/doku.php?id=comparisons, but it is specifically aimed at network backup software comparable to Amanda and Bacula. It's not exhaustive.

You can also look at the links here: http://www.linuxquestions.org/bookmarks/tags/backup

Personally, I like Amanda a lot, and it is what I use for a complex environment of servers with a tape library on a backup server. My backup server has multiple network interfaces to connect to a backside GigE network that my newer servers are on as well as the regular network where the older servers are on 100MB network. It juggles simultaneous connections all across the network pulling in backups to a pair of 300G holding disks before pushing them out to the tape library. It drives my tapes at maximum speed, because it is staged and that step is local.