Do you have to make Airline/Hotel/Car reservations through Delta or can you purchase through Expedia? Specifically do you have to purchase through Delta to accumulate MQDs? Or can that also be through Expedia since the bill comes from Delta?

I've been happy with Expedia because not only can you take advantage of their rewards program, you can usually get great vouchers if you're inconvenienced during your trip by any of the flights/hotels/cars you purchase.