When I want a specific make or model car, I usually rent from Hertz. This is the one advantage that they offer that National does not... although I find their rates higher on average than National. It's not often that I'm in the mood for a specific car (e.g. once in Hawaii I reserved and rented an Audi A3 cabrio), usually I prefer to just take my pick from the EA.

Sometimes, I will have multiple reservations... an EA ressie from National and then a specific make/model ressie from Hertz. If I don't find anything I like on the EA, I know I have my specific car reserved at Hertz as a backup. I then just call and cancel the ressie I didn't use.

Last year I wanted a convertible at MCO. At the time, the convertible choices from National were lame (VW Beetle or PT Cruiser), so I had a Mustang ragtop reserved at Hertz just in case. Sure enough, there were only a couple beat-up PT's at national, so I went with the Mustang. It was a little more money but way worth it.