I tend to work the Entertainment and other deals as aggressively as I can to try to get either National or Hertz. Avis has also been straightforward, though I'm put off by the way their website handles coupons. They often tie with Hertz at a price level (even after competing coupons), and Hertz wins those.

Am not a great fan of Alamo because of practices like not quoting the standard rate when you have a coupon entered on the website (They usually jack it up to negate the coupon value), and the $10.99 late-fee/retroactive charge surprise they pull on you at the time of rental. These are easily avoided if they'd choose to play it straight, and are too reminiscent of worst industry practices. Alamo used to be notorious for telling you one thing over the phone and another at the counter; I guess they can't be as bad about that with people waving printouts at them, but their culture hasn't rid itself of the bad elements. I hope it doesn't bleed over to National.

Enterprise lost me with the insurance bit. I don't know if they still do it like they did, but all the unnecessary hassle is a great way to drive off customers for good.

Others have been hit and miss; have been lucky not to run into the big negatives but they also haven't had great positives.