Where should you base yourself on the French Riviera?
Nice is the most useful place to stay on a first Riviera trip. Cannes and Antibes lie west of the city; Monaco and Menton are east, and regional trains make day trips in both directions straightforward. Antibes is better if you want a smaller old-town stay, Cannes if the seafront resort atmosphere is part of the holiday, and Menton if you would rather slow down at the quieter eastern end of the coast. Monaco is usually better visited for the day.
Full answer
The Riviera is easier to picture as a string of towns along the coast. Nice sits near the middle of the places most first-time visitors want to see, with regional trains running west towards Antibes and Cannes and east towards Monaco and Menton.
That makes Nice the easiest place to unpack once and explore from. You can spend the day elsewhere and still come back to a city where dinner, a walk through the old town or an evening by the sea does not feel like an afterthought.
Antibes is the stronger alternative if you want a smaller old town and somewhere that feels less urban. Cannes makes sense when the seafront, resort hotels and polished evening scene are part of what you came for rather than something you only want to see once. Menton, farther east, suits a slower coastal stay when its old town and quieter pace matter more than seeing the whole Riviera.
Monaco is usually better visited than used as your place to stay. Sleeping there puts you at the eastern end of the trip, making outings to Antibes or Cannes longer. Unless Monaco itself is the focus, Nice leaves more of the coast within easy reach.
If you want to see a lot of the Riviera, stay in Nice. If one particular town is where you most want to wake up, eat dinner and spend the evening, stay there and accept a little more time on the train.