A HSA is the best legal tax dodge available. Max it out!
The HSA is the only triple tax advantaged program.
1) You don't pay taxes on contributions.
2) You don't pay taxes on investment gains.
3) You don't pay taxes when you withdraw it.
But, to qualify for the triple tax advantages, you must spend it on medical expenses at some point in your life. That doesn't seem like a very high hurdle.
401k, IRA, Roth IRA, etc. pale in comparison to an HSA since all of those other items make you pay taxes at some point. So, if you have an HSA available, and if the HSA makes sense for you, then max your contributions and milk the tax savings.
To maximize the HSA tax savings, I contribute the max, and then pay for medical bills out of pocket (note: even if you pay out of pocket, you still get the low insurance negotiated prices). Why would I want to reduce the value of something that grows tax free? Also, doing so lets you avoid fees at almost all HSA providers (usually there is a $3000 or $5000 minimum balance to avoid fees, so you have to max it out at least at the beginning or the fees destroy the whole tax savings). Leave the money in the HSA for years/decades to build up as much of the tax savings as possible. Then use it for your medical expenses when you are retired (save medical receipts then).
That said, HSAs tend to have limited investment options and higher investment fees. So be careful. For example, it is not easy (or often not even possible) to invest in the low cost Vanguard funds in an HSA.
You also have to do the leg work. The point of the HSA is to make the consumer shop around for good prices. Since you are paying for medical expenses out of pocket, or eating up your tax advantaged pile of money, minimizing the medical expenses is really in your best interest. But the whole medical field is set up to hide prices from you. The same service or the same drug may be 10x more across the street. But, you won't know unless you go to both doctors or both pharmacies in person to find out (good luck ever getting a price on the phone, you usually will just get the run-around). That can be quite a hassle. In exchange for this work, you get triple tax advantages and insurance premiums that are generally much, much cheaper than any other insurance.
One of my biggest disappointments this year is that my wife's employer dropped the HSA option and my employer doesn't have an HSA option either. My tax bill for 2016 will skyrocket by thousands of dollars and I have to pay ~$1500 more during the year for insurance. I gain nothing in exchange.