The HSA has two beneifts that the Roth does not have:
1) HSA money completely avoids the FICA tax rate of 7.65%. Unless I am mistaken, if you withdraw for income after 65%, you will only pay income tax on it. Your Roth money is taxed with income and FICA tax when you earn it.
2) If you use the HSA money at any point in time for medical expenses, you avoid any income tax on it. You can use it to pay for Medicare premiums. This money will not be taxed when you contribute it to your HSA, it then compunds over time, and then if you use it for medical costs, it is not taxed then. The tax advantages of this are freaking awesome.
The disadvantage is you can't use it for income until you are 65. But, if I could only do one or the other, it would be the HSA. I will have health care costs at some point in time. The tax advantages are too good to pass up.