Browsing the interent suggests both RH and [public.com](http://public.com) have the same and the lowest margin rates I could find. IBKR is often mentioned, but still higher than the prior two.
I already have a Robinhood account, but I'm not exactly a fan of the interface that appears to be tailored for cell phone interactions. I have no experience with Public. In either case I'd need to transfer the assets, from Fidelity. I have reached out to my Fidelity advisor, but I only give them 1-2% chance of offering a rate that would prevent me from moving.