I know for beginners, many folks will use Google or Word Reference. Then folks start to use Collins, which I've never really liked. Since my French reading level is somewhere around intermediate (I can muddle through YA novels), I prefer to skip the bilingual dictionaries unless I'm actually going from English to French. My favorites are:
Centre National de Ressources Textuelles et Lexicales
Provides curated definitions, etymology, and usage examples from several different
respected sources, and is inclusive of all recognized French dialects, since one of their
sources is Laval's Panfrancophone research center.
The traditional standby, the Britannica and OED of French. But they are rather snobby
and sometimes downright inaccurate when it comes to, ah, colonial Frenchs. Also has
a bilingual dictionary.
That's all I have. Anyone else have handy French resources?