I've never had a really bad car, new or used. With older cars I expect they'll have problems and try to anticipate them. New cars should be solid for at least the first few years. Having said that....
1994 Dodge Intrepid ES 3.5L, bought new, very nice when new but the car aged quickly, paint chipped easily, windshield cracked easily, interior showed wear, transmission shifted badly even after a couple of fluid flushes. I dumped the car after 2 years and 50,000 miles.
2000 Saab 9-5 SE, turbo V6, fantastic driving car but needed some expensive work (oil cooler seals, SID, etc) that was thankfully covered under warranty. It was a lease and I turned it in after 3 years & 40,000 miles. Part of me wishes I kept it, the other part feels the car would be have quite expensive to maintain. Probably a good thing its gone.
1994 Infiniti Q45, bought used in 2006 with only 37,000 original miles, car showed a lot more wear than its mileage, I knew it would be an expensive car to maintain and it was, fortunately had an awesome specialty shop to fix it but still.... $300 tune ups and $600 injector replacements can wear out ones wallet.