^
My understanding is that the difference in DV and DVCAM is the head pitch, which is what dictates the image quality, and ultimately DVCAM does indeed provide a better image than DV. I have used the PD170 in both modes, in addition to many other DV and DVCAM cameras, and I have yet to see footage that I shot in DV look as good as DVCAM. That may be due to the varying chip sets in the cameras, or the brand of tape. I'm not a tech, so maybe there's some test that proves me wrong if you put them up on scopes or something, but in my experience I have consistently found that DVCAM looks better than DV.
As for the HVR-Z1U, no it doesn't do an actual 24p, but it does 1080i, 50i or 60i which all look pretty good. It also does 16:9 native, whereas the Panasonic does a "fake" letterbox. It provdes the same effect, but doesn't allow the same flexibility.
I didn't mean to say that Panasonic's 24p was fake, in the sense that it wasn't actually 24p. What I meant was that you could record in 24p on a miniDV tape, and have the image in that mode on the tape, and it would play back as such in any miniDV deck, as opposed to other HD cameras, which need to be downconverted (like the high-end Sonys). I didn't mean to say that as a negative thing, rather as a nice feature.
Anyway, they're all nice cameras, and I can't afford any of them, but if I could, I'd go with the new Sony. It gives you the most flexibility, and it would play tapes from either of the other two.