My previous employer had a discount exclusively with National, and we got Emerald Club for free, so I have some experience with that. I also like the ability to pick your car, although sometimes (especially in Chicago) I have detested the mad rush off the bus to run and grab the "best car". If they ALL had CD players, or they were all non-smoking, then it would be better because you could choose based on external looks, but they don't. I was always happy with National service, including the one time a unlicensed driver side-swiped me and crashed the fender.

My current employer has 10-20% off deals with Avis and Hertz, including membership in Preferred and #1 Gold, and I've had a chance to experience both of those. Avis sometimes has "your name in lights" (like SFO, where they have a new sign that I couldn't find last time I was there, until I was directed to it) like Hertz, which is nice. Avis in ORD usually has the car running, while Hertz has the car under a cover. I have been getting Camrys from both of those in ORD lately, which is good from a fuel efficiency point of view but it's not the most powerful car for I-294 passing.

National has continued to extend my Emerald Club membership, even last year when I didn't rent from them. If it's a leisure rental, what I normally do now is to go to each of these three web sites, put in my dates, and pick based on price. As far as I'm concerned, they're equivalent for what I want. (I'm not particularly picky about the type of car, as long as it's intermediate or better, and I'm assured of that by all 3 programs).