It depends on what enviroment you are considering and the data being backed up (daily,full ,etc)I had the dlt-vs80 which is 40/80 and it did a modest job, BUT was not reliable. it comes with a 3year warranty and hp service is next to none. I had mine exchanged 4 times and after some discussion with hp they upgraded me for FREE to the ULTRIUM drive 200gb . this is pure sweetness. no problems with tapes or cleaning issues. I have used dat,dlt but will never go back .sold on the hp LTO.
If you do decide LTO the tapes like any other are not cheap, I checked around and the prices ranged around 50 to 71 bucks each. shop shop shop. I did and got the hp tapes from INSIGHT.COM for 26 bucks each.
Jim