Since the end of the year, Sosh, B & You and SFR RED have generally agreed to start their promotions around 12 / month, but there are still a few points of difference to make your choice.
At the moment, B & You offers for 13.99 / month a package which includes 60 GB (including 10 GB in Europe / DOM) plus unlimited weekends. If you consume a lot of data on weekends, this can be interesting. Unlimited internet is valid in mainland France from your mobile (excluding multi-SIM option) , which a priori excludes connection sharing.
Bouygues Telecom does not yet support eSIM for the iPhone, but that will change in the spring.
Otherwise, Sosh always offers 50 GB (5 GB in Europe / DOM) 9.99 / month for one year (then 24.99 / month) and SFR RED 60 GB (8 GB in Europe / DOM) 12 / month.