8 mm
wasn't bad.  At about that time, we were heavily involved in
 specifying tape for customers and we tended to rank things this way:
 DLT > 8mm > 4mm DAT > Travan > QIC.  
 Interesting.  That's about my assessment too, though I don't use tapes
 all that much. 
 
Personally I'd rate it a bit different.
DLT > 4mm DAT > QIC > 8mm
I don't remember ever dealing with Travan, though I think I have a couple
drives in the collection I've built at work.
Zane