Hi Adriana,

I have a friend who is using Orange SIM card in his mobile and he is very happy with the services. 

Since last year there is no roaming fees in Europe and it become very advantageous to take a French SIM card instead of Swiss that are very expensive. If you subscribe for a 1 year abonement its alaways more attractive than to take a pre-paid card. I would advice you to come to the local mobile shop in France and ask them if you can stop your 1 subscription before the expiration in case you will be leaving Europe before. Sometimes its ok. You can check the prices here : https://boutique.orange.fr/mobile/forfaits-orange

Here is very detailed information about data volumes: 

https://en.selectra.info/broadband-phone-france/guides/mobile-phone-how-much-data-needed

Good sites that compare many things, including mobile subscription/abonements

https://www.bonus.ch/Telecom-Telephonie-Mobile/Comparatif-abonnement-reseau-telephone-mobile.aspx

https://en.comparis.ch/telecom/mobile

If you dont make alot of calls, also might consider using a prepaid with data. then you just manage the data , either using free wifi in many locations or just the prepaid dataplan.