H3 and S2 are kinda similar, except by using hexagons, H3 grid centroids are equidistant - rectangles have different distances from center to center.

H3 also has efficient means for finding a cell’s neighbors, and comes with some nice algorithms - like the “compact” fill. See https://uber.github.io/h3/#/documentation/overview/use-cases

The hierarchical search data is built into a grid’s ID in both H3 and S2, which helps when comparing ID’s to see how close they are to each other.

For visualization, I prefer the way H3 looks over S2. While that’s just an opinion, H3 grid is exposed directly to drivers and in lots of tools.

I work for Uber and have used H3, but don’t work on the library.