If you book at the last minute, you may see some significant differences.

For example, I’ve seen Travelocity offer hotels that expedia doesn’t offer. Expedia had an Expedia special rate hotel as their lowest priced offering, while Travelocity had a lower priced hotel in the same class that Expedia didn’t show, and IIRC, Expedia had offered that other hotel room a couple of weeks previously.

Also, Hotwire can give you a hotel room at a price that is significantly less than Expedia or Travelocity, but you don’t know exactly which hotel you’ll get.