Which car should I buy? (Budget 12-15,000)

Hello dear friends, I’m new here in the forum and would like to ask a question at once. I’m standing in front of my first (own) car purchase and can’t quite set myself yet. My budget is at the top and I’m tending to an Audi A4 year 2009-2010. My desired criteria are: – Limousine (Audi a4, bmw 3 or Mercedes C class) – Diesel (is diesel worth it at all?) – max. 150,000 KM – Automatic gearbox – part or full leather equipment I drive about 150km a week, therefore I don’t know exactly whether a diesel is worth it. I don’t know exactly. The questions I have are: Which car is the best for my needs? I don’t pay so much attention to the PS number. I put more value on interiors, so it’s more worth getting a newer year of construction with less power. Is this assumption right? Are there any known defects in this category or has anyone had bad experiences? I have heard the e Electronics quickly breaks down in the audio models. I’m looking forward to your answers and I hope I didn’t ask too many “Newbie” questions :-). Greetings from Hesse.