Ckcoles,
I am not familiar with either 2 headsets. I would be considering "robustness" and whether you can repair them in-field. I suspect you'll be doing some bush flying and they'll probably get kicked about. I know my DC's did.
That would be something I would be looking at + after sales service. Ideally, you shouldn't need it, however, the real world isn't a glossy brochure.
I now use Bose A20 (bizjet operations). Love them. I have used Sennheisers in the past and they were brilliant, but I have found that the Bose are much better (so they should be, twice the price!).