We booked with hotwire a week before our trip from 12/5-12/13 (8 days). My searches landed me at $200 for a mid-size using various coupons. Hotwire's prices was $154 (all taxes included) for midsize so I thought we'd go for it. We booked it and got Hertz.
Hertz has a shuttle you take to the rental agency, not on-site. We checked in smoothly and opted to go for an extra driver at $65 extra. We got a brand new Chevy HHR with 2 miles on it. It fit our 3 suitcases great and was roomy in the front. I'm not familiar enough with cars to know if this was a standard mid-size or bigger but it was great for 2 adults, 2 kids, 4 carry-ons and 3 suitcases.
I don't think I had the option to add a driver when I bought on hotwire, I think it was your basic, 1 driver, unlimited miles package. So the extra cost was a little high but circumstances required we needed 2 drivers.
I was happy with it and I would do it again. I've used hotwire a lot for motels and such and I am satisfied with how the system works.
I never priced 2 drivers on the other sites because I didn't know we would need that. That's the only note I will make of in the future but I would do it again.
Returning the car was very smooth, we were back at the airport shortly.
Good luck with whatever you decide.