In France, the "best job site" is to know someone who can introduce you personally to the employer, preferably the hiring manage. The personal touch has always been key in France. But as far as job hunting sites, it varies greatly from one employer to the next which ones they use, consult and trust.
In any event, you won't get a job offer strictly online. Ideally, you would need to make yourself available for interviews - which may mean springing for a trip to France (or wherever) including obtaining a visa (probably a tourist visa). Remember that for any EU country, you are standing in line behind any similarly qualified candidate from anywhere within the EU and EEA - if only because they don't need a visa nor a work permit.
In some of your other posts, you mention recruiters. Normally, the best way to come to the attention of recruiters is simply to apply for jobs being posted by recruiters. If you meet requirements for either the posted job or for other positions they want to fill, they will get in touch with you. But you have to show them that you are aware of requirements like visas and work permits and give them an idea of why an employer would go the extra mile to hire you over a local candidate.
Cheers,
Bev