I went through a pretty exhaustive search for the best HSA with requirements being no fees with as low a minimum as possible, and reasonable fund selection when I left an employer with an HDHP and crappy HSA plan, and joined a new employer with unfortunately for me, fantastic benefits and no HDHP option. Ultimately I went with Health Equity for my rolled over HSA. The minimum you need to keep in the savings account portion is $2500 to avoid any fees, and they have reasonable mutual fund choices. Note that none of the fund choices are what I would call low expense ratio or passively managed, but I suspect that Health Equity survives by a spread on the expense ratio. Still, I think it ends up being a better deal for the relatively low amounts I'm keeping with them. Not that anyone on this forum ever has a real health need :) but their customer service is great, if I were to ever need to pay for any healthcare costs out of it.
No referral or incentive here, just found them to be the best option from those I surveyed.