If available to you you should max out an HSA (and it's not even close.)
The HSA has three main advantages over all other options.
1. You can contribute pretax money (better than a Roth)
2. You can pull out money tax free for health expenses at any time ( better than a traditional IRA/401K.)
3. It is portable. (unlike most 401K/403 Bs) so if your employer picked out a bunch of high cost actively managed funds for you to choose from you can just transfer your money to a different low cost provider and invest in a cheap vanguard fund, (or whatever you prefer.)
The key is to do all of your health care spending with out of pocket dollars and to allow your HSA stash to grow tax free. Each dollar that you spend on health care, dental care, vision, becomes, in effect, a dollar invested in a Roth with pretax money. There is nothing sweeter for a super saver like you.
It is truly a thing of beauty.
I have written this stunning savings vehicle extensively including here...
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Enjoy!
-Alexi