I know that I had the option of the FSA or HSA at my place of work. I chose the HSA because of the carry-over. It really depends on what/how you expect to have medical bills. If you know that you will need a large lump-sum early in the year (like the dental work) the FSA might be better as you get access to all of your contributions on Jan 1. But, if you think/feel/believe that you won't need early-in-the-year access, the HSA might work better since any contributions you make to it can carry forward to future years, where the FSA has to be completely used (I think by March 31 of the following year, but I could be wrong).
The essential difference between the two as I understand them is that FSA gives immediate access but is "use it or lose it", while the HSA slowly builds a reserve that you can keep until it is used up - even into retirement.
On a completely unrelated note - for those with family members with fins, fangs, feathers, or fur PetCo is celebrating their 50th year and has some really good sales through Oct 10. $5 of purchases of $50 or $15 of $75, plus lots of things are 10% off (or better) and most dog and cat foods are offering a free bag of treats with a purchase of a bag of food. I just bought about 3 more months of food and treats and saved a touch over 20% total (and I didn't even get the treats for free - one of my girls can't handle glutens and the food I buy was not one of the qualifying bags for free treats. If it had qualified, I would have saved about 30%). Since it was stuff I knew I needed to buy anyway, I figured now was the time to buy it.
Just wanted to share for others.