Fabfilters recently came out with a new desser -Pro-DS. I have their Pro bundle (Compressor, Limters, EQ, Gate) and they are my goto plugins for precision control. (I tend to use the UAD plugins for color.) I am mixing two songs (The Story and Someday Soon) with a new soprano. She's not terrible on sibilance, but as you can imagine, those songs benefit from some help. The stock plugs that I have aren't that bad, but I downloaded the Fabfilters demo to give it a go. Excellent plugin . Just dead easy to use for controlling sibilance in vocals. Of course, like most Fabfilters plugs, it has a ton of other features, but they always make the basic features really easy to use and don't let the "advanced" features get in the way. Very transparent and easy to use. Knocked down the sibilance in a very natural and transparent way.

Check out the tutorial by Dan Worrall - who posts here as IIRs. Very well done.