Planning on doing this with wife and 2 kids. Has anyone ever done this and have any specific recs or advice? Nicola gets the most/best reviews but is also the most expensive. And I keep going back and forth between a full day or half day, afternoon or morning...? Want to see the sights from the water, swim, eat/drink, etc. Appreciate any recs.

Beaulieu Boat Charters. They're based out of Beaulieu-sur-mer about 25 mins east of Nice.

https://www.beaulieuboatcharters.com/

Unsolicited recommendation: We "discovered" a new restaurant for us in Nice last summer - Bistro de JAN. South African chef whose main restaurant next door is Michelin-starred. The bistro was so good (food and atmosphere), I don't think we need anything more. Going back a few weeks from now. Also trying out chez Apopino this trip.

Thinking of hitting both the Chagall and Matisse museums which we've somehow missed on past trips to the area. Anyone have feedback on those?

cant help with any boat recommendations, but one thing to think about is you might enjoy the beach clubs in Antibes, just down the street from Nice.... get a few chairs, swim, drink, eat....