I'd go with DAN simply for the fact that they're the most widely accepted form of dive insurance. I choose DAN after reading several posts from individuals on this board who had the unfortunate need to use their DAN insurance. Their response was that DAN took care of them with very few, if any hassles. In some circumstances, DAN was the only form of dive-specific insurance recognized.
A few additional points as well:
Your DAN membership ($29- which you'll need to get their insurance) goes to fund additional hyperbaric research, and DAN is widely considered the leader in this field of study. They maintain the dive industry's only 24 hour diving emergency hotline (available to non-members as well), and they'll also throw in Alert Diver magazine, and online access to their dive accident database. This is a good deal in and of itself.
PADI's just doing what they always do... nipping at the heals of an already successful program to try and get a piece of the pie. In my opinion, the best Virginia and Buckley plan that PADI offers gives you just a little more coverage (but not by much) than DAN's coverage, the cost is higher, and the overall set of benefits is smaller.
With DAN's insurance plan, $70 goes to pay the insurance company, and $29 goes back into research to make our sport safer. To me, that sounds a lot better then $99 straight into V&B's coffers.
-B.