National's Emerald Club is the best rental car program on the market.

After 10 rentals in a calendar year, you get Executive status, which gives you access to the "Executive Selection" with guaranteed upgrades (pay the intermediate rate for a full-size or higher). After 25 rentals in a calendar year, you get Executive Elite status, which guarantees a car for you at any National location with 24-hour notice, even in sold-out situations, and for an extra fee your National car can be delivered to you at a general aviation airport within 50 miles of a National counter.

As Executive Elite, you earn free rentals three times faster than Hertz. Every five paid rentals gets you a free day valid at any location, with no capacity controls and no drop-off fees if you're renting one-way. I use all my free days for one-way rentals, where they can save hundreds of dollars. As Executive Elite, the free days even work for renting Luxury cars, such as the Cadillac DeVille (though this seems to be either an unpublished benefit or a glitch in National's system; normally the free days apply only to full size or Executive Selection vehicles).

Granted, National doesn't have a Prestige Collection like Hertz, but for the intermediate rate you can pick from a whole array of full-size cars or better in the Emerald Aisle or Executive Selection. Most airports put some premium vehicles, SUVs and minivans along with the full-size cars in the Executive Selection, and as long as the car is in that area you can rent it at the intermediate rate if you're Emerald Exec or Exec Elite. Even the standard Emerald Aisle usually has a diverse offering of vehicles. National's cars are mostly GM with a few Chrysler Corporation products thrown in. The Pontiac G6 (Emerald Aisle) and Buick LaCrosse (Exec Selection) are currently "exclusive" to National, and both have XM satellite radio and sunroof for no extra charge. Personally, I prefer the Chrysler vehicles such as the Sebring coupe and Jeep Grand Cherokee.

At locations with an Emerald Aisle/Exec Selection (most major US airports), the car rental experience couldn't be faster. Either walk or take the shuttle bus to the National lot, pick the car of your choice from the aisle, and drive to the exit booth with your driver's license and Emerald Club card. Within a couple of minutes, you'll be out of the rental facility with no need to stop at the counter.

I chose National over Hertz at first just because National was the only top-tier agency willing to take my business; I'm an under-25 frequent renter for both business and pleasure. But even once I turn 25 (or sue Hertz and Avis for age discrimination) I'll probably stick mostly with National because I enjoy the ease of choosing my own car from the lot, the generous free upgrades, and the low rates. Check on the National board here on FlyerTalk for some contract ID# that can provide some big savings. Most of the time, when I've checked Hertz rates for others, National comes out cheaper, especially for one-ways.