Depends on how long you plan to drive and or keep it. I like to purchase my used cars under 100K, like 75-90K to keep cost down and then drive it another 10 years.
I look for the price point where the car depreciates a good bit but still has a lot of miles left on it. I like used cars that have 30,000 or less but for cars that have a really good reputation I will go up to 75,000. Buying a car that is a few years older but has really low miles can be the best value in a used car.
The lower the better , logic as follows, most new cars depreciate the minute you drive off the lot (Please advise if I'm wrong here), lower the millage, newer the car. Imagine finding a 1956 stingray convertible well preserved with 39 miles on it,, to stretch a point, but not without some merit. Now how about a AMC Rambler with 98K vs, one with 129 Miles.