Worlds apart, superset provides powerful visualisation capabilities, but is very difficult to use/setup/maintain (although they just launched as a company [0], so perhaps that will change).

Metabase is a very easy to use data exploration, data vis and reporting tool designed to give insights into data in an easy/self service way for mostly non-technical users.

I've POC'd both, and would recommend Metabase or redash unless you really know what you need out of superset

[0] https://preset.io/blog/2019-10-09-series-a-announcement/