Which car brand is better, Acura or Mercedes-Benz?

My mom is wondering what kind of car would be good to replace her Mercury Grand Marquis. She was considering the Lincoln MKS but after we heard it wasn't that great of a car (and all our Ford products have been unreliable) so my mom is considering either an Acura RLX or Mercedes-Benz E-Class. Looking at used ones, they're about the same price, but we might be able to get a better deal on the Acura. Which car would you get?

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