"I am looking for a very lively town with shopping, restaurants & nightlife."
IMO, that fits Cannes and why it's probably being recommended, but if those were my "wants," I'd also look at Nice and Antibes. Shopping is probably going to be best in the larger cities of Cannes and Nice, but from anywhere along the coast, you can get to the other resorts very easily. Trains run along the coastline and they are frequent. Antibes' close neighbor, Juan les Pins, is probably where you will find nightlife center if you chose that resort and I would think of those locations together. See what others have to say.
BTW and another IMO, we would probably buy in Cannes because we enjoy the abundance of restaurants that have a view of the water and are easily accessible if you are in proximity of "La Banane," the part of Cannes that is near La Croisette. This part of Cannes is relatively flat and access to the transportation depots is generally an easy walk. The Palm Beach section of Cannes is where you will find a hub for "nightlife," but there are also clubs around La Croisette. However, that's what would work for us and others will feel just as strongly about their favorite resort. Balance the opinions, decide what works for you, and go with your instincts.