The last time we bought (in 2002) we went certified, pre-owned from a dealer. As someone else mentioned, it was a good compromise. The car seemed brand new, but had 23K on the odometer.
We have never bought from Hertz or any other car rental agency, but that is certainly something to think about.
We have only bought new one time in our life. The problem with buying new is that there may be no record on reliability, especially if they've made changes to the make/model you are considering.
That car we bought certified, pre-owned is a 2000, so it is now 14 years old. It still has life, but we are now researching the reliability of current models we might consider so in two or three years when it is time to purchase, we'll already have a pretty good idea of what to consider and what to cross off the list.