As everyone else has basicially said, go DLT. Since I assume Ultrium is out of your price range...

Biggest reliability reason why DLT is better is that the data part of the tape never touches anything beyond the other parts of the tape while wound around the spool. Even the recording head dosen't make direct contact, it hovers. Thus heads last much longer, and there isn't a few rollers inside the tape drive contacting the data part of the tape.

For those wondering what Ultrium is, it's basicially a slightly better DLT technology. Same single spool idea, but a much improved pickup method (avoiding the DLT problem of dropped leaders), and a data chip inside the tape that stores the table of contents, allowing a much faster seek time. Native capacity of Ultrium is currently at 200gb uncompressed.

Price wise, you might look into DLT VS80 drives. These use the same DLT IV tapes that other 40/80 GB DLT drives use, but they store data on them in a method that allows the drive to be cheeper, as it dosen't move the head around.