Full disclosure, when I go to Europe it's for work, not vacation, so my perspective may differ. And as much as I love virtually the entire country of France, I really can't recommend Marseille. Any of the excursions in the surrounding areas that have been mentioned would make a much more enjoyable day IMHO.
Naples ... yes, it's dirty and noisy, and I LOVE it. 🥰 Partly because the southern part of the country was "home" to me, and it just encapsulates the essence of urban southern Italy which I happen to love. That being said, yes, the surrounding areas also have some really worthwhile stuff. But I wouldn't be scared away if you enjoy the urban vibe--I think NYC is a good comparison. Marseille is, of course, also urban and dirty and noisy, but to me it just doesn't feel like France. Naples, on the other hand, oozes Italy. 🙂