It usually has lower deductible and it's a nice way to lower your AGI. That said, the HSA is likely better in every other way.

If you want to use it as an investment vehicle, you are kind of crazy to not take advantage of an HSA. It's probably the best investment vehicle that exists. Tax free on the way in and tax free on the way out (For qualified expenses). Plus tax free growth.

I'm not sure either will help you more than the other with tax deductions. Unless you have an unused amount at the end of the year in the FSA that you lose, then I believe you can deduct that amount (which is just minimizing a loss, and not ideal).