HSA Authority (part of Old National Bank). Last time I ran the numbers, the break-even point on annual expenses vs some other options was about $10k in HSA balance — where smaller balances would pay more at HSAA than some other provider(s). But they cost less than other providers for larger balances (again, last time I checked).
https://www.oldnational.com/thehsaauthority
And for comparison, https://thehsareportcard.com/hsa-authority / https://thehsareportcard.com/the-top-10-investor-hsas-1 . The landscape may have shifted since the last time I did my research.