How much data are you backing up?
My advice - STAY AWAY FROM DELL. That said, let me also add, it's been about 5 years or so since I last used Dell Backup Hardware regularly. At that time (and for several years prior, I had used abotu 8-10 different Dell drives - some SDLT, some DDS3/4, some DLT (never LTO in fairness) and of those, I probably had 5-7 of them fail at some point during the warranty period. To me, this was a REALLY high failure rate and frankly, my trust in Dell backup hardware was destroyed. We switched to Overland brand systems... and though we had an initial firmware bug, once that was sorted out, those Overland SDLT systems were flawless for at least 3 years. (Our data centers had very clean power and dozens to hundreds of servers - and everything was conditioned through UPS... this was NOT bad power going into the tape drives).
(So go with the Quantum. MAYBE Dell fixed their tape drive issues - or maybe they never applied to LTO... but in either case, I think you are taking a huge chance going with a Dell brand tape backup system - and possible a tape backup system at all - again, how much data are you backing up and are you under any kind of regulatory and company policy that requires archiving backups over a period of years?)