General questions on the possible purchase of new cars

Hello! Since the current car is getting a bit older and several repairs are increasing, I wanted to ask questions before buying a new car and know your opinion on certain topics, because you often hear different things: – If you compare a sandero with a more expensive small car like the Fabia, where do you recognize most deficits? Similarly equipped they cost 12k or 19k and now I wanted to know whether this is more the longevity, material, workmanship or other How are cheaper manufacturers such as Kia or Hyundai to assess? Are they in between or are they all the same nowadays? – At the VW Group, I keep hearing that there are still enormous problems with the DPF. Is that part of the past or is that still the case today that problems arise when short distances are often left behind? Is it true that the French are less affected by this? – What is the oldest car that is found in today’s vehicles? Diesel engine? Is this the dci k9k engine or are there older ones? – What do today’s cars do better than the current ones about 10 years ago? Are these simply consistent developments and the biggest differences in the equipment found or especially in the safety, consumption and the chassis? Personally, the last three points don’t seem to me really enormously improved. If I sit in a Clio 3 or a current polo, it doesn’t seem to me as if d he is better at these points about worlds or how do you see it? I’m all about the expert opinion of others to see which vehicle you should save on. I’m grateful about different views. Sg