Seat Ibiza (pre-VW), the one with Porsche engineered on it. You couldn't demist the windows it was so pathetic, the heater element was so low spec clearly designed for Spain not the UK. Everything was so cheap about it, very low grade plastic and not a very efficient car, very low mpg. Looked nice though parked up. Also had a Vauxhall Vectra with electrical issues which was a right pain. However also had a Vauxhall Cavalier before it which was fantastic and loved to bits. I've had 3 original mini's, not without a few issues here and there but still remember them fondly for the simple joy of throwing them around corners with their go kart handling and how 30mph felt like 50mph when you are so low to the ground. Those were probably the last cars that I attempted to repair myself and replace parts myself. It just seemed to get really complicated after those.
However my best car is my current car which I've had approaching 12 years from new and done nothing to it apart from basic servicing. The first fault I've had has just occurred, the light behind the fuel gauge sometimes goes off but for the last few drives it hasn't so maybe its corrected itself perhaps a bit of water ingress. However I should point out I'm a very low mileage driver and have only just passed 20,000 miles in the car, less than 2,000 miles per year. I'm still debating whether to replace the engine timing belt which is meant to be good for 100,000 miles but perhaps not 12 years of light use. It's the non turbo engine though which is much easier on the timing belt I believe. It probably only have 3 more years of use before its completely run its course I feel with very little value. I like to drive cars into the ground pretty much. It was only about £7k new because Chevrolet left the UK market so they were heavily discounting the model, it was £17k originally.