(Hmmm, forgot to Cc: this to the list...)

As Brian's mentioned, Amanda is designed to handle full and incremental
backups on her own (yes, I refer to Amanda as 'her,' I'm one of those
'anthropomorphing' types...).  Where, yes, it may be a bit harder for
you as a human to track (not being able to say 'Yes, there was a full
backup of everyone last X'), Amanda handles this load balancing between
full and incremental backups well, is good at her internal management,
and when needed for a restoration, she'll tell you what tapes she needs.
 This allows you to have a collection of tapes of uniform size, rather
than keeping track of different sized tapes for different backup levels.

Coming from the world of Arkeia, I was of the 'everything has full
backup at the same time' opinion myself.  But after some gentle drubbing
about the head from other folk on the list, I came to understand the Zen
of Amanda: 'Let Amanda do her own thing, and all will be well.'  I've
been happy with how Amanda handles her backups ever since...

It really is a question of what you need.  While Amanda is great for
(imho, ymmv of course) changer devices, desktop backups (to recover from
user 'ooops' mistakes, all backups maintained on site), there are some
things she may not be the best for (ie. say, server backups, when you
need to take tapes off location w/ full backups in case of
fire/flood/etc and want to cram as much full backup on as few tapes as
possible).  While Amanda -can- do this with some tweaking, it isn't
necessarily what she was designed for, so another tool designed with
that mentality may be better.

Me, I run Arkeia for server backups (only 3 servers that absolutely
-have- to be backed up off site, so the 'Lite' version fits the bill
quite nicely), and Amanda for desktop backups (via Samba mounts) that
stay in-house for a 4-week cycle of tapes.  Figure out your
backup/restore/storage/retention/etc. needs, and work from there.  Do
you need storage off site?  Then maybe software with more strict full
and incremental delineations would be better.  Are backups going to be
kept on site and/or you need instant access to them at any given time?
Then maybe the load-balancing of Amanda would be better to help with
tape management.  Or perhaps a mix of the two...

Determine what you need, then find the best tools for those needs.

As for tape drives, you asking about a range smack dab between my own
experience areas (DDS-3 and -4, and LTO-2), so I can't give you much
help there...

Best of luck getting it all figured out...