Based on your descriptions, I don't think you'll be happier at any other rental company, especially when you state that you have had problems with 10 out of last 12 rentals. Here are some info for you to make your next rental experience easier:

1. Hertz IAD has hundreds of cars and most agents are very friendly. They even drive me back to the airport, if I am late.
2. I don't understand why you drove a faulty car for 30-60 minutes. You should have noticed the issue after max 5 minutes after leaving the lot, and return.
3. You can switch out a car at any Hertz location. Just show up and switch, if you have a problem with the car. That's true for all rental agencies.
4. Local Edition do not fill up the gas. It's always "return with same gas level" on all rental companies, in my experience.
5. If you have an issue, low brake fluid etc, just drive to nearest location and switch. Better is not to even accept and leave the lot in the first place.
6. Smoky/dirty cars. Why did you accept those cars and drove away from the lot? Go back to the office and switch directly.
7. Check on your Hertz status, especially since you state that you average 225+ rental days per year.
8. Arriving late and that they have given away your reserved car is unacceptable. Should never happen to someone with status. What location was this?