I used to be working for BMW and they ahve shit reliability, audi is not as bad but its pretty bad.
Lexus doesnt cost too much to repair plus it rarelly break
Infinity has one of the best price/performance/look for the money (In my opinion) good reliability
Mercedes has bad reliability
Porche isn't too bad
Honestly no reason to buy a "luxury" car anyway unless you get hard when people look at your car,
Id rather have full loaded honda or or toyota. Or an old rare japanese car.