Transportation tips from Rome hotel to FCO airport and also CDG airport to Paris hotel

Traveling light 1 bag or able-bodied:
Rome the Train Leonardo Express + metro + walk
Paris the RER B train + metro + walk.

You can take Uber, public transportation, taxi. When I have luggage I prefer an Uber or a taxi. I've done both in Paris. No experience in Rome but Uber is there.

In Paris we took a private transfer from SunTransfer. It was fine, but we could have saved money by taking the RER B train. The train/metro is very easy to use! We never felt unsafe during our 6 days using the metro system in Paris. Check online to see how close your hotel is to a metro stop. If I had to do it over again, I would use the train and metro.

In Paris there are flat rates from CDG to a Right Bank location (50€) or a Left Bank location (55€). To me, going directly to the taxi rank, ignoring anyone who walks up to you and asks if you want a taxi, and having the taxi line manager direct you to a cab is absolutely the safest. For me it’s the least hassle as well. I do use the Metro all the time once I am sightseeing, just don’t want to mess around going up/down stairs with a suitcase-even a 20” wheelie.

Paris does not have a strong shuttle culture and there are always threads on Trip Advisor complaining that a pre-booked shuttle didn’t show. Seems the pre-booked/pre-paid are the worst.

I’m not up with Uber but I understand there are issues with where they can legally pick up passengers at CDG.

Where are you planning to go in Paris? With the address one of us can tell you if RER/Metro combination would be straightforward.

It really depends upon your circumstances, which is better.
1. Once you have three or more people, then taking a taxi may be just as expensive, since you don't pay per person. With the train, you pay per person. In both Rome and Paris, there is a fixed rate from the airport to the city (however, check the details since in Rome, city is defined as within the walls of the city).
2. Depends upon how much luggage. If you have more than just one suitcase and backpack per person, then lugging all that stuff can be a hassle. In Paris, it is a relatively long walk from the customs exit point to the train. It is also a considerable walk from the train stop to the metro stop, at least at Gard du Nord. Also, in Paris, if you need to change Metro lines and haul your luggage a considerable distance from the Metro stop to the hotel, then a taxi may be better.
3. The train is not subject to traffic jams, like taxi or buses. We took the bus from the airport to Paris and was stuck for nearly an hour at one intersection due to an accident. So, the train is the fastest way to get into the city. However, once you are in the city, depending upon the location of your hotel, it may take significant time to get from the train station to the hotel. This is particularly true if you are not familiar with the city and metro system.
4. The trains and metro system in both Rome and Paris are relatively safe. Need to stay alert for pickpockets. Also, some instances of people trying to steal suitcases/backpacks/purses on the metro and trains. Taxi is probably safer overall, but not that much more.

In both cities, I asked the hotel to reserve a taxi. About 7 am, the traffic is not so heavy...in both cases, I arrived in 30 minutes or less. 50 - 55 Euros.

I would take a taxi. For a couple of reasons — 1) If your hotel isn’t near the train station, even though train fare may be the cheapest option, you still have to get from hotel to the station with your luggage. 2). If your flight is early in the morning, you may fine that public transportation isn’t available early enough in the morning to get you to the airport in time enough to allow check-in, security, etc.

Taxis are available 24/7 and can pick you up at your hotel and handle your luggage.

Please provide some more details! How many people are you? Where are you staying? Are there children/elderly/disabled people? Traveling with one rollaboard or ten steamer trunks? Is your hotel in central Paris or out in the boonies?

These kinds of questions are difficult to answer when no other details are provided -- the answer provided to a 29-year-old solo traveler with a backpack and small roll-aboard traveling to a hotel 100 meters from Gare du Nord ("take the RER") is not going to be the same as the advice to a family of four with two small children and tons of baggage going to a hotel near the Eiffel Tower ("take a taxi"). It's impossible for us to guess all the relevant details.

The OP is looking for the safest, quickest way to get from airports to hotels, not from hotels to airports. I don't know Rome, but in Paris the short answer is the RER "B" train connecting with whatever Metro line(s) get you closest to your hotel. That will most likely be faster than any surface transportation, and it will be safe as long as you keep an eye out for pickpockets and luggage thieves on the train.

You didn't ask about cost, but the RER-Metro combination will also be cheaper than any alternative for a single person. But, as others have noted, a shared taxi will cost little or no more for a group of four. To the extent convenience is a consideration, you might consider a taxi, or the bus service to various rail stations (Le Bus Direct), or a combination of RER to Gare du Nord plus taxi to the hotel.

For ease and comfort you can't beat a taxi. There are "taxi" signs as you exit the airport. Just walk out the door and there is your ride. With luggage, that's the way I go now that I find moving my luggage too much work. Having said that, I did take the Leonardo Express from the airport to Rome last year. It was easy. I bought a ticket in the airport as I walked through, then took a short walk outside to the train.