You probably want the Carre d'Or, which is roughly the neighborhood bounded by the Promenade des Anglais, Blvd Gambetta, Blvd Victor Hugo, Ave Jean Medecin and Ave de Verdun. You can go slightly beyond those boundaries by a few blocks to the NE of Place Massena and North into Musiciens. Just avoid being directly on Rue Massena (Pedestrian Zone) or the Promenade des Anglais (unless you are on an upper flow on the Prom). However, you'll be close to the pedestrian zone and not far from the Old Town (across the Promenade du Paillon). The large 18+ nightblub is in this district, along the Prom.
You could also try directly in the Old Town, but there are three things to watch for: noise on certain streets and squares, lack of elevators and lack of AC. The periphery is quieter, except along the water/Pescheurs where all the cafes and bars are lined up. The Port is a backup choice.