The only advantage the JB3 would have over DAT in "generational" thinking would be the miniscule chance that the DAT has problems being read during the playback>transfer process. Sure you may have a good tape, but if your playback deck has problems, then those problems will be part of the transfer.
With the Nomad, and perhaps other HD recorders, this "transfer" has already been done when the info was recorded to the internal HD. Sure there may be problems during the transfer from the internal HD to you computer's HD, but more than likely not...
Is one better than the other? I'd actually say they each have pros and cons vs. the other:
DAT is proven and works very well. JB3 is new and can be tempermental. DAT is obsolete, HD recorders ar ethe new wave. DAT is known to be Bit-Perfect, JB3 allows fast transfer.
"Better" is subjective. As a person wth exp. with both, I like the Nomad 3 a lot, but would love to have an M1 or D100 as my main recorder. I like the functionality, the proven track record, etc...
Terry