It's honestly a hard call! Now I feel like I'm spreading myself between both platforms, which is tiring and perhaps less effective. I do think Medium has more "discoverability" potential - i.e. its editors seem to be more proactive about finding and sharing new talent. I'm still getting far more reads/views on Medium, even though they still vary wildly story by story. Substack seems to be more of a long-term play that enables you to build a consistent audience. I think it takes more patience but will probably prove more valuable over time.
Appreciate you reading and sharing my Substack story! Best of luck!