I have never rented from Dollar but I have used Enterprise once. I will NEVER use Enterprise again under any circumstance.
They have horrible customer service, very sub-par cars, and push the extra insurance so much. When I was shown my car I immediately said I had rented a midsize and the agent told me that was a midsize (it looked like an economy) and had more miles on it than any other rental I've had. I had to sign 3 or 4 times to decline the insurance, and once more while I was sitting in the car before driving off. The agent told me my credit card would not cover me (which is incorrect, but an unsuspecting customer may be fooled). Never again!
I prefer National and Hertz. They have new cars with low miles. A lot of my cars have under 2,000 miles, the lowest was only 300 miles. I've NEVER been pushed to get the extra insurance. Usually I don't even see an agent, and if they do ask its simply a question -- no arguing or lying. Avis is also very good.
Haven't used Enterprise in Orlando, but locally in San Diego they have been excellent (several times over the past year). Dollar on the other hand was terrible the one time I tried them, and I'll never use them again. National is my preference, but only because of Emerald Aisle at locations that have it.