Bought mine new, absolutely no regrets. My wife's Jeep Commander was bought used (1 yr old w/ 15k miles), also no regrets. We plan on keeping both until the wheels fall off.
Some cars are just better off buying new (resale for my Camaro is still pretty close to what I bought it new), and other's you can get for 15-20% cheaper if you can accept it being 1-2 years old with decent miles. I think we bought my wife's Jeep for $16k (granted it's the entry-level "Sport" V6 model).
Hell, I'm even looking at picking up a decent used mid-90's Jeep Wrangler for under $3k.
IMO the key is finding the car you want, figuring out how long/how much you plan on using the car, then finding the cheapest way to get said car. I never recommend "settling" for a car, simply because, in my experience, you tend to not like the vehicle as much and consequently tend not to take care of it.