Juan les Pins, in my experience, tends to have clearer waters than Antibes beaches in mid-summer, although that depends on the prevailing winds. As the two towns are on opposite sides of the Cap, there’s a good chance that if one side of the headland is a bit murky then the other will be clear. However, if you want crystal clear waters and a tranquil day out, then pack a picnic and hop on the short ferry ride over to the stunning Cannes islands, Les Isles de Lerin.
Stingers do sometimes plague Riviera beaches, but luckily some lovely soul maintains a jellyfish alert website, updating recent sightings of jellyfish along the Côte d’Azur. Check it out here - it’s in French, but it’s pretty easy to understand: it has big red jellyfish marked on the map, or green flags where it’s good to swim.