Going to Nice later this month and had originally rented a car but I keep hearing that traffic is terrible in the summer. The plan was to use the car to drive to Monaco, Cannes, Eze, St Tropez, etc...Should we opt for Taxi or Train instead?

I wouldn't rent a car in Nice any time of the year. Use public transportation.

I think a car would be a good idea for really exploring, especially back away from the coast, and traffic usually flows, even if it can be somewhat slow sometimes -- but aren't you on holiday anyway? Parking can be more of a problem, if you are the impatient type.

A taxi wouldn't solve the traffic problem, although it might lighten your pocketbook.

And the train doesn't even go to St. Tropez.

Agree with kerouac; it will be busy, but I always drive in that area in summer, and though it is sometimes slow, I prefer it to taking the train. There are some beautiful roads to drive, the Corniche between Nice and Monaco, and the Esterel from Cannes to St Raphael.

Driving to St Tropez is a nightmare in summer though; could take you three hours from Nice. Unless you go very early in the morning, like 7 am. Tuesday and Saturday are market days, and extra busy.

Drive...the trip is sometimes as much fun as being there.
Just don't go to St Tropez. That drive in July or August is NO fun.

I believe there is a boat that goes from Cannes to St. Tropez. Gets you out of traffic and you see wonderful coastline.
Otherwise, be prepared for a long time for the commute.

You can explore back into the hills north of Nice by train, the little Train des Pignes: www.provencebeyond.com/travel/railpignes.html

Nice has such good transportation connections (train and bus) that I'd forget the car. On the other hand, if I wanted to drive, I'd stay somewhere other than Nice.

It depends on what you want to do. If you will focus just on Nice and one or two other places on the coast train will probably work best.

If you want to explore several of the sights and smaller towns up in the hills (which I highly recommend) a car is almost a necessity.

I have used hire car + my own car throughout France - except for one area..Nice.
Bus transport in Nice excellent - one euro no matter where you want to go - as far as Menton or Cannes, trains are also very frequent and reasonably priced. Tram journey in Nice is also one euro - www.lignedazur.com

It's not having the car that would be a problem: it's parking the car in Nice. If you stay outside the city the parking becomes less of a problem.