We will be leaving on a 7-day NCL cruise out of Marseille this June. We will be spending either 2 or 3 nights before the cruise in Paris, plus 1 more night after the cruise. For the night before we depart from Marseille: would you prefer to take a train to Marseille the day before and spend the night there, or would you prefer to spend the night in Paris and take a train the morning of (cruise departs in the afternoon) and why?
I'd say stay in Marseilles. You don't want to take a chance on a travel disruption causing you to miss your cruise departure. And Marseilles is worth a day.
I'd choose Paris because 2-3 nights is way too little time there. Two nights is one day. Paris is amazing and wonderful, you won't want to leave.
I'd take an evening train to Marseille and see a bit of the city in the morning before boarding the cruise ship. I'd also add more time in Paris, if at all possible.