(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...
