I guess we should differentiate between regular hotel (and car and flight) bookings compared to "opaque" bookings where you don't see the name of the provider.
For regular bookings, the major hotel chains seem to have figured out it is in their interest to offer the lowest prices directly (for the identical room / conditions). A while ago, I would go to a couple of different aggregating sites, and be able to put in a claim with the chain using their best rate guarantee and get a nice discount while booking direct. Now, I generally don't bother and mostly just shop on price and quality amongst the chains that I prefer. I also have lots of hotel points and do the calculations about when to pay cash or use points. One discount I have found is that anything in the Hilton chain can have about a 10% discount compared to other hotels when using Citi's ThankYou points. I've gotten some superb rooms at great prices that way.
For opaque bookings, Hotwire has the advantage of being able to specify children in a hotel booking. Priceline only guarantees double occupancy. I used Priceline once for a one night hotel stay and the hotel was really bad and clearly did not meet the standard that they advertised (they compared it to several brands of the major chains). They refused to do anything about it, and I never used them ever again. That was 12 years ago.
My Hotwire bookings were fine but I never got anything that exceeded my expectations of the discounted price I received. I only booked with them when I was travelling alone on non business trips. With family, I want to be sure of what I'm going to receive and on business, there is no reason to take chances if you're personally not saving money but bearing the risk of a problematic hotel.
Some people use hotwire and priceline extensively and there are ways to figure out what hotel you are going to receive and many people have gotten great bargains. I can understand the attraction when trying to book high end properties but I've often found that there's a reason why a hotel that is in the category of $400+ hotels can be had for $200. I'd much rather choose where I'm staying and I have the option of using points when they make sense which is usually for the high end properties (as well as the lower end ones).
I've never used Hotwire or Priceline for "opaque" airline tickets but I did for car rental. I think there is little risk of a quality problem with "opaque" car rentals compared to hotels and the prices can be attractive. But for several years now, I've never found them to be cheaper than either going direct with some good codes or going through Costco. There are also some advantages with choosing the car rental company such as going directly to your car if you have membership.
