Mercedes-Benz ML400: is it worth getting a used one or should I look at the new GLS?

I'm considering purchasing a used ML400 but also eyeing the new GLS. Pros of the ML400 include lower purchase price, decent fuel efficiency and ample interior space. However, its age means older safety features and possibly outdated infotainment systems. Meanwhile, the GLS boasts modern tech and more refined ride but comes with a higher price tag and increased running costs