I like Hertz. Of course, since I'm not old enough to operate a rental car, my parents have to be going with me on vacation. When they go on vacation, their attitude is, "We paid for the damn vacation so we should rest and Matt should drive." When we're on vacation with a rental car we do a LOT of driving so we get a big old Crown Vic with the V-8. I love that.
For me, if I'm picking up a car at an airport where the rental companies share a common lot, I'd make reservations with virtually every one of them, and then take a browse around the lot to see who has the more "interesting" vehicles before I head for the rental counter. No way am I going to spend my money to get stuck behind the wheel of such 4-wheel abominations as Taurus, Century and Lumina.
My family has had trouble with getting frequent flyer mileage credited properly with Alamo, so more recently they've preferred Avis. Enterprise (though they don't participate in the ff programs we use) and Dollar have been good as well.