Are the HDV's really HD? Isn't their maximum resolution 1440x1080 vs AVCHD at 1920x1080? Mentally, I would be more comfortable with the tape since it is a built in archive, but is it really a 'future' proof option vs the newer format? I think it is a tough call the HDV's are bulkier than the AVCHD's as well from the consumer perspective.
As long as there is software to edit HDV, the concern about futureproofing is moot (assuming your gear doesn't break). As soon as you buy a camcorder, you're locked into the quality that said camcorder produces. For instance, if you buy an AVCHD camcorder today, any advances in AVCHD tomorrow won't improve your footage. The only question you need to ask yourself is whether 1440x1080 HDV looks better/worse than 1920x1080 AVCHD at the time of purchase.
The new Canon's can record AVCHD at 24 Mbps, I think. HDV is at it's 25 Mbps limit and there's no signs of any improvement (I haven't heard any rumblings of an HV40).
I'd say that right now, HDV and AVCHD are pretty close. At least close enough where the differences in codecs is moot and it becomes a comparision in hardware (i.e. lenses, physical size, etc).
So getting back to the issue of future-proofing, I guess you do have a little more future-proofing in terms of supported hardware/software if you go with AVCHD, but I would guess that HDV will be supported for many years to come ... assuming that Macs still have Firewire
