Marseille to Nice

To me, the "easiest" way between Marseilles and Nice is train, by far. Traveling the "best" way is somewhat subjective. (You might prefer driving...not me.)
Takes about 2:36 or so and costs 36€ - 38€.

Cheapest is bus. Takes about the same time and costs 1as little as 8€.

Coast route by car takes about an hour more (I'm guessing).

I don't know about the other cities.

Steve

Train! Except for Saint Tropez.

The train ride from Marseille to Nice is GORGEOUS. It follows the coast from Marseille to Toulon, then goes inland for 25 minutes and then back to the coast until Nice. Make sure to sit or reserve a seat on the right hand side of the train. Also if you take a TGV, there are two levels. The lower level is easier with luggage, is a quiet zone, and closer to the WC. The upper level is how people move between cars, no noise restriction, and you have a staircase to deal with. A very kind French woman showed me how to "hide" my rolling bag in the triangular space created by two seats back-to-back. This is a safer place to keep your luggage than at the end of the car in the racks.

Trains are very frequent along the Marseille - Nice route.

Once you are based in Nice, there are hourly trains to Monaco, which is 20-30 minutes farther to the east. I also suggest taking the train just past Monaco and visiting Menton.

Cannes is going in the other direction from Nice (west) and again there are very frequent trains. Trip is about 30 minutes. I highly recommend a few hours in Antibes, which is between Nice and Cannes. Charming town with a Picasso museum.

St. Tropez is on a peninsula so there isn't a train station right in town. It will involve a bus or bus/train combo. ST is 2 hours from Nice and 3.5 hours from Marseille.

Train tickets can be purchased in advance on www.sncf.com.

Without knowing what you are thinking of doing while in Marseille, I would suggest only 1 night there and four nights in Nice.

And finally the car traffic along the Cote D'Azur can be a nightmare during the summer. Train travel is much more relaxing and not prone to traffic congestion.

Bon Voyage!

I've driven Nice to Monaco, Nice to San Remo and back, it's easy enough but if you don't like endless tunnels, frequent tailgating, dangerous overtaking (and undertaking) and excessive speed then I wouldn't recommend it. Driving in Monaco itself can be a pain if you're not familiar with the area.

I would opt for the train.

All of the coast is most convenient by train. For the places you mention, train is easier than a car. Traffic makes driving a big hassle. At least with a bus, you're not doing the driving but can get stuck in the same near-gridlock traffic. If you want to get away from the coast for part of the trip, car becomes the better option but only for that excursion.

The train is your best bet to travel between Marseille and Nice -- unless you are comfortable driving in and out of city traffic (the tollway inbetween is relatively easy - the driving in the cities is what can be stressful the first time). As noted previously, there is no train stop in St. Tropez. You must connect by bus (or ferry). It's best reached by car, and traffic in July/August in and out of the peninsula can be a nightmare (but far easier the rest of the year).

Most of your destinations are reachable from Nice, so it is advisable to switch one of your nights over from Marseille. With transit and your departure day, you really only have one full day. The bus (#100) from Nice to Monaco is another option to the frequent trains, with a nice view. People sometimes combine this with a trip to the villages of Villefranche-sur-mer (train or bus) or Eze (#82/#112). The train is the superior way from Nice to Cannes -- Antibes can be a free stopover on the return.

Thank you so much everyone, for all your comments!

A few summers ago, we took the train from Marseille to Nice. In Nice, we booked a boat to St Tropez. I am not sure what you all are looking for in St Tropez, but for my husband and me, we thought it was over rated. Keep in mind, we were there in summer and it was HOT- that may have contributed to our views on it. We absolutely loved Nice and Marsielle was lovely, but out of the 3, Nice was by far our favorite.