Max out HSA or a Roth IRA first each year?

Yes, an HSA could act like a stealth IRA.

I'd start with ROTH as depending on HSA administrator you may not have the same flexibility of investments, fees etc. Not to mention the possibility of having that option canceled by your employer. But if you can invest in the same things they are pretty equal but still ROTH due to possibility of income phase outs, higher amount you can contribute if single, and such.

Basically, there should be less BS with a ROTH.

Answer may change if you have a higher allowable HSA contribution for families or really think you'll use the money a lot. That wasn't my personal experience so I'm not good for that.

An accountant or something should show up shortly.

My opinion assuming equal investment options is to go with the HSA. With an HSA, there is a possibility that money will never be taxed (used as a medical expense, it is funded pre-tax and untaxed coming out as a medical expense). At worst, assuming no early withdrawals, it will act as a traditional IRA starting at age 65. Also, if funding an HSA, I think it's better if you fund it using payroll deductions as in some plans, it may be exempt from Social Security tax.