I would go with Amanda for a variety of reasons. Run down through the bookmarks here http://www.linuxquestions.org/bookmarks/tags/backup
. There are several for Amanda. Check out "Ten Things I Like About Amanda".
I have a few installations with tape libraries that hold 16 AIT5 tapes and either one or two drives (that's a total of 6.4TB native and whatever the vendor claims for compressed). I run a 6 week rotation of tapes and periodic archives, so I do have to shuffle tapes occasionally. What I like most about Amanda is that it just works. Amanda's intelligent planner smooths out system and network loads and tape usage over the span of the dump cycle (one week for me), and Amanda takes into account and recovers from a variety of error situations that might stop other programs.
There has also been a steady surge of high quality development work going into Amanda over the last couple of years.