I am in month 1 of FIRE, and I spent a week choosing one. I chose Lively, a new internet startup. The bank account is FDIC insured at Choice Financial, and investments are at TD Ameritrade. Their big selling points are customer service, a host of features online, and small fees. You need $1000 to start investing, but you don't need to keep anything in cash. As with a bank account, I can change if I don't like it.
For those who have not shopped for an HSA, it is like choosing a credit card or a bank, but most of the choices are terrible. There are few clearinghouses to help you choose one, and many details are completely opaque.
My old company used Payflex, and I personally do not pay maintenance fees or investment fees. I think they charge $3/mo and $1.5/mo, respectively. Their choice of funds - 4 funds + 4 fund of funds - is weak. Their website is also pretty cryptic. My money has not grown much over the last 5 years.
I relied on the Can I Retire Yet review
https://www.caniretireyet.com/best-investing-hsa/, and a handful of googled reviews. I liked the HSA report card, but I cannot tell whether the reviewer is worth listening to.
https://thehsareportcard.com/the-top-10-investor-hsasMy BCBS plan partnered with HSA Bank, and the above reviews rated them bottom half. That is probably good compared to most, but they have $90 per year in fees if you want to invest in low cost funds and ETFs, $2 ATM, $10 checks, $25 closing fee, $6 debit card, and some others. They do not require you keep money in cash. Most require $1000.
Vanguard recommends Health Equity, because they use Vanguard funds exclusively. They have about $50/year fees plus 0.40% custodial fee, and similar special item fees similar to HSA Bank. Need to keep $2000 in cash. No Thanks!